STRO 10-K & 10-Q changes, risk factors and insider trading

Investing in our common stock involves a high degree of risk. Before making your decision to invest in shares of our common stock, you should carefully consider the risks described below, together with the other information contained in this annual report on Form 10-K, including our financial statements and the related notes and “Management’s Discussion and Analysis of Financial Condition and Results of Operations.” The risks and uncertainties described below are not the only ones we face. References to past events are provided by way of example only and are not intended to be a complete listing or a representation as to whether or not such factors have occurred in the past or their likelihood of occurring in the future. Additional risks and uncertainties that we are unaware of, or that we currently believe are not material, may also become important factors that affect us. We cannot assure you that any of the events discussed below will not occur. These events could have a material and adverse impact on our business, financial condition, results of operations and prospects. If that were to happen, the trading price of our common stock could decline, and you could lose all or part of your investment.

We are ana earlyclinical stage biopharmaceuticaloncology company with no products approved for commercial sale. We have a history of significant losses, expect to continue to incur significant losses for the foreseeable future and may never achieve or maintain profitability, which could result in a decline in the market value of our common stock.

We are ana earlyclinical stage biopharmaceuticaloncology company. Biotechnology product development is a highly speculative undertaking and involves a substantial degree of risk.

We will need substantial additional funds to advance development of our product candidates and failure to obtain sufficient funding may force us to delay, limit or terminate our product development programs, commercialization efforts or other operations. We may have difficulty accessing additional capital on reasonable, or even any, terms to continue our product and platform development or other operations and have made and may have to make again in the future difficult prioritization decisions regarding development and potential partnering of our clinical and preclinical product candidates.

Since our inception, we have invested a significant portion of our efforts and financial resources in research and development activities for our preclinical and clinical-stage product candidates and the development of our technology platform, including our in-house manufacturing capabilities.platform. Preclinical studies and clinical trials for our product candidates have required substantial funds to date and will continue to require substantial funds to complete. As of December 31, 2024,2025, we had $316.9$141.4 million in cash, cash equivalents and marketable securities. We expect to incur substantial expenditures in the foreseeable future as we seek to advance multiple product candidates through clinical development, manufacturing, the regulatory approval process and, if approved, commercial launch activities, as well as in connection with the continued development of our technology platform and manufacturing capabilities.platform. Based on our current operating plan, we believe that our available cash, cash equivalents and marketable securities will be sufficient to fund our operations through at least the next 12 months. However, our future capital requirements and the period for which we expect our existing resources to support our operations may vary significantly from what we expect, and we may need to seek additional funds sooner than planned. Our monthly spending levels vary based on new and ongoing research and development and other corporate activities. Because the length of time and activities associated with successful research and development of our product candidates is highly uncertain, we are unable to estimate the actual funds we will require for development and any marketing and commercialization activities for approved products. For example, the timing and amount of our operating expenditures will depend largely on:

the costs associated with the development of our internalexternal manufacturing and research and development facilities and processes;

the cost of pursuing and timing of obtaining regulatory approvals;

our efforts to enhance operational systems and hire and retain key personnel, including personnel to support development of our product candidates and satisfy our obligations as a public company; and general economic, industry and market conditions, including market volatility, high levels of inflation, changes in interest rates, changes in tariffs and trade restrictions, uncertainty with respect to the federal debt ceiling and budget and potential government shutdowns related thereto.shutdowns.

If we are unable to obtain funding on a timely basis or on acceptable terms, we may have to delay, reduce or terminate our research and development programs and preclinical studies or clinical trials, limit strategic opportunities or undergo additional reductions in our workforce or other corporate restructuring activities.activities beyond the reductions in our workforce announced in March 2025 and September 2025. We also could be required to seek funds through arrangements with collaborators or others that may require us to relinquish rights to some of our technologies or product candidates that we would otherwise pursue on our own. We cannot provide assurance that anticipated collaborator payments will, in fact, be received. We do not expect to realize revenue from sales of commercial products or royalties from licensed products in the foreseeable future, if at all, and, in no event, before our product candidates are clinically tested, approved for commercialization and successfully marketed. To date, we have primarily financed our operations through payments received under our collaboration and other associated agreements, the sale of equity securities, debt financing and a royalty monetization agreement. We will be required to seek additional funding in the future and currently intend to do so through additional collaborations and/or licensing agreements, public or private equity offerings or debt financings, credit or loan facilities, royalty monetization or a combination of one or more of these funding sources. Additional funds may not be available to us on acceptable terms or at all.

If we raise additional funds by issuing equity securities, our stockholders will suffer dilution and the terms of any financing may adversely affect the rights of our stockholders. If we raise additional funds through licensing or collaboration arrangements with third parties, we may have to relinquish valuable rights to our product candidates, or grant licenses on terms that are not favorable to us. In addition, as a condition to providing additional funds to us, future investors may demand, and may be granted, rights superior to those of existing stockholders. Any future debt financings, if available, are likely to involve, restrictive covenants limiting our flexibility in conducting future business activities, and, in the event of insolvency, debt holders would be repaid before holders of our equity securities receive any distribution of our corporate assets. Adverse macro-economic conditions, including volatility in equity capital markets, fluctuating interest rates, tariffs, actual or perceived instability in the U.S. and global banking systems, and fluctuations in foreign exchange rates, could prevent us from raising additional capital in sufficient amounts or on terms acceptable to us, or at all. Failure to obtain capital when needed on acceptable terms may force us to delay, limit or terminate our product development and commercialization of our current or future product candidates, which could have a material and adverse effect on our business, financial condition, results of operations and prospects.

We have no products on the market and allmost of our internal product candidates for cancer therapy are in preclinical development, including ourSTRO-006 mostand advanced candidate, STRO-004.STRO-227. Additionally, we have programspartnered-programs that are being evaluated by partners in clinical trials and by us in earlier stages of discovery and preclinical development and may never advance to clinical-stage development. Our ability to achieve and sustain profitability depends on obtaining regulatory approvals for and successfully commercializing our product candidates, either alone or with third parties, and we cannot guarantee you that we will ever obtain regulatory approval for any of our product candidates. We have limited experience in conducting and managing the clinical trials necessary to obtain regulatory approvals, including approval by the FDA. Before obtaining regulatory approval for the commercial distribution of our product candidates, we or an existing or future collaborator must conduct extensive preclinical tests and clinical trials to demonstrate the safety and efficacy in humans of our product candidates.

product-related side effects experienced by patients in our clinical trials or by individuals using drugs or therapeutic biologics similar to our product candidates;

inability to obtain alternative sources of supply for which we have a single source for product candidate components or materialsmaterials, if necessary;

failure to demonstrate in our clinical trials a sufficient response rate or duration of response or other applicable clinical endpoint, which can be unpredictable even in light of earlier non-clinical and clinical data;

unfavorable FDA or other regulatory agency inspection and review of one or more of our clinical trial sites or the manufacturing facilities of our CMOs;

delays and changes in regulatory requirements, policy and guidelines, including the imposition of additional regulatory oversight around clinical testing generally or with respect to our technology in particular; and varying interpretations of our data by the FDA and similar foreign regulatory agencies.

Our business is dependent on the success of our product candidates, including STRO-004, STRO-006 and STRO-227, which are generated from our proprietary XpressCF® and XpressCF+® platforms. Existing and future preclinical studies and clinical trials of our product candidates may not be successful. If we are unable to commercialize our product candidates or experience significant delays in doing so, our business will be materially harmed.

We have invested a significant portion of our efforts and financial resources in the development of our proprietary XpressCF® and XpressCF+® platforms and our proprietary product candidates, including STRO-004.STRO-004, STRO-006 and STRO-227. Our ability to generate commercial product revenues, which we do not expect will occur for many years, if ever, will depend heavily on the successful development and eventual commercialization of our product candidates. We have not previously submitted a new drug application, or NDA, or a biologics license application, or BLA, to the FDA, or similar regulatory approval filings to comparable foreign authorities, for any product candidate, and we cannot be certain that our product candidates will be successful in clinical trials or receive regulatory approval. Further, our product candidates may not receive regulatory approval even if they are successful in clinical trials. If we do not receive regulatory approvals for our product candidates, we may not be able to continue our operations. Even if we successfully obtain regulatory approvals to market our product candidates, our revenues will be dependent, in part, upon the size of the markets in the territories for which we gain regulatory approval and have commercial rights. Our revenue may also be dependent, in part, on any third-party collaborator’s ability to co-commercialize such product candidate or to commercialize any companion diagnostic for such product candidate, as applicable. If the markets for patient subsets that we are targeting are not as significant as we estimate, we may not generate significant revenues from sales of such products, if approved.

We plan to seek regulatory approval to commercialize our product candidates both in the United States and in selected foreign countries. While the scope of regulatory approvals generally is similar in other countries, in order to obtain separate regulatory approvals in other countries, we must comply with numerous and varying regulatory requirements of such countries regarding safety and efficacy. Other countries also have their own regulations governing, among other things, clinical trials and commercial sales, as well as pricing and distribution of our product candidates, and we may be required to expend significant resources to obtain regulatory approval and to comply with ongoing regulations in these jurisdictions. We cannot predict the likelihood, nature or extent of government regulation that may arise from future legislation or administrative action, either in the U.S. or abroad.

The success of STRO-004STRO-004, STRO-006, STRO-227 and our other future proprietary product candidates will depend on many factors, including the following:

successful enrollment of patients in, and the timely completion of, oursuccessful clinical trialstrials, including in compliance with the FDA’s GCPs and any additional regulatory requirements from foreign regulatory authorities;

establishing successful technology transfers and collaborations to develop our product candidates with potential licensees, obtaining and maintaining patent, trademark and trade secret protection and non-patent exclusivity for our product candidates and their componentslicensees;

achieving and demonstrating desirable therapeutic properties for our product candidates’ intended indications;

maintaining an acceptable safety and efficacy profile of our product candidates through clinical trials and following regulatory approval; and achieving commercially relevant success in the market post approval.

Additionally, we have in the past and may in the future create benchmark molecules for comparative purposes. For example, we have created a benchmark FRαTissue Factor, or TF, targeting antibody-drug conjugate, or ADC, using conventional technology that results in a heterogeneous ADC mixture.technology. However, we cannot be certain that any benchmark molecule that we create is the same as the molecule we are attempting to recreate, and the results of the tests comparing any such benchmark molecule to any other potential or current product candidate may be different than the actual results of a head-to-head test of any such other potential or current product candidate against a competitor molecule. Additional preclinical and clinical testing will be needed to evaluate the therapeutic index of our potential or current product candidates, and to understand their therapeutic potential relative to other product candidates in development. While we believe our ADCs may be superior to other investigative agents in development, without head-to-head comparative data, we will not be able to make claims of superiority to other products in our promotional materials, if our product candidates are approved.

If we do not achieve our projected development goals in the time framestimeframes we anticipate and project, the commercialization of our products may be delayed and our stock price may decline.

From time to time, we estimate the timing of the anticipated accomplishment of various scientific, clinical, regulatory, commercial and other product development goals, which we sometimes refer to as milestones. These milestones may include the commencement or completion of scientific studies and clinical trialstrials, and the submission of regulatory filings. From time to time, we may publicly announce the expected timing of some of these milestones. All of these milestones are and will be based on numerous assumptions. The actual timing of these milestones can vary dramatically compared to our estimates, in some cases for reasons beyond our control, such as health epidemics and pandemics, government shutdowns, natural disasters, global instability and geopolitical conflicts within regions where our clinical trials are conducted. For example, we may open clinical trial sites in jurisdictions that may face enrollment, operational or other difficulties due to conflicts within the region. In addition, we rely on third party vendors, contractors and consultants to provide services in connection with our clinical trials. If these third parties do not perform their services in a timely or workmanlike manner, our clinical studies may be delayed. If we do not meet these milestones as publicly announced, or at all, the commercialization of our products may be delayed or never achieved and, as a result, our stock price may decline.

Our approach to the discovery and development of our therapeutic treatments is based on novel technologies, including unprecedented dual-payload ADC technology, which includes Immunostimulatory Antibody Drug Conjugate, or iADC, and dual Antibody Drug Conjugates, or ADC2 technology,ADCs, that are unproven and may not result in marketable products.

Our current and prior product candidates have been tested in a relatively limited number of clinical trial patients. We may ultimately discover that our XpressCF® and XpressCF+® platforms and any product candidates resulting therefrom do not possess certain properties required for therapeutic effectiveness. XpressCF® and XpressCF+® product candidates may also be unable to remain stable in the human body for the period of time required for the drug to reach the target tissue or they may trigger immune responses that inhibit the ability of the product candidate to reach the target tissue or that cause adverse side effects in humans. We currently have only limited data, and no conclusive evidence, to suggest that we can introduce these necessary properties into these product candidates derived from our XpressCF® and XpressCF+® platforms. We may spend substantial funds attempting to introduce these properties and may never succeed in doing so. In addition, product candidates based on our XpressCF® and XpressCF+® platforms may demonstrate different chemical and pharmacological properties in patients than they do in laboratory studies. Although our XpressCF® and XpressCF+® platforms and certain product candidates have produced successful results in animal studies, they may not demonstrate the same chemical and pharmacological properties in humans and may interact with human biological systems in unforeseen, ineffective or harmful ways. These unknowns and other emerging findings from our clinical trials and preclinical studies may result in protocol amendments, which may result in additional costs and may also delay our anticipated clinical timelines.

Results of our clinical trials could reveal a high and unacceptable severity and prevalence of side effects or unexpected characteristics. Undesirable side effects could result in the delay, suspension or termination of clinical trials by us or regulatory authorities for a number of reasons. In our clinical trials to date, our product candidates have been generally well tolerated, and the most common treatment-emergent adverse events, or TEAEs, that resulted in a treatment delay or dose reduction were reversible neutropenia and myalgia/arthralgia. It is possible that, as we test our product candidates in larger, longer and more extensive clinical trials or as the use of our product candidates becomes more widespread following any regulatory approval, illnesses, injuries, discomforts and other adverse events that were observed in earlier trials, as well as conditions that did not occur or went undetected in previous trials, will be reported by patients. If such side effects become known later in development or upon approval, if any, such findings may harm our business, financial condition, results of operations and prospects significantly.

If product candidates based on our XpressCF® and XpressCF+® platforms are unable to demonstrate sufficient safety and efficacy data to obtain marketing approval, we may never succeed in developing a marketable product, we may not become profitable and the value of our common stock will decline. The regulatory approval process for novel product candidates such as ours can be more expensive and take longer than for other, better known or extensively studied product candidates. We are not aware of any company currently developing a therapeutic using our approach to ADC, iADCADC or ADC2dual-payload ADC development and no regulatory authority has granted approval for such a therapeutic. We believe the FDA has limited experience with therapeutics in oncology or other disease areas developed in cell-free-based synthesis systems, which may increase the complexity, uncertainty and length of the regulatory approval process for our product candidates. For example, our ADC product candidates contain cleavable or non-cleavable linker-warheadlinker-payload combinations or novel warheadspayloads that may result in unforeseen events when administered in a human. We and our existing or future collaborators may never receive approval to market and commercialize any product candidate. Even if we or an existing or future collaborator obtains regulatory approval, the approval may be for targets, disease indications or patient populations that are not as broad as we intended or desired or may require labeling that includes significant use or distribution restrictions or safety warnings. We or an existing or future collaborator may be required to perform additional or unanticipated clinical trials to obtain approval or be subject to post-marketing testing requirements to maintain regulatory approval. If the products resulting from our XpressCF® and XpressCF+® platformplatforms prove to be ineffective, unsafe or commercially unviable, our entire platformplatforms and pipeline would have little, if any, value, which would have a material and adverse effect on our business, financial condition, results of operations and prospects.

The outcome of preclinical studies and early clinical trials may not be predictive of the success of later clinical trials, and preliminary results of clinical trials do not necessarily predict success in future clinical trials. Many companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in late-stage clinical trials after achieving positive results in earlier development, and we could face similar setbacks. The design of a clinical trial can determine whether its results will support approval of a product, and flaws in the design of a clinical trial may not become apparent until the clinical trial is well advanced.advanced or completed. While certain relevant members of our company have significant clinical experience, we in general have limited experience in designing clinical trials and may be unable to design and execute a clinical trial to support marketing approval. In addition, preclinical and clinical data are often susceptible to varying interpretations and analyses. Many companies that believed their product candidates performed satisfactorily in preclinical studies and clinical trials have nonetheless failed to obtain marketing approval for the product candidates. Even if we, current or future collaborators, believe that the results of clinical trials for our product candidates warrant marketing approval, the FDA or comparable foreign regulatory authorities may disagree and may not grant marketing approval of our product candidates.

In some instances, there can be significant variability in safety or efficacy results between different clinical trials of the same product candidate due to numerous factors, including changes in trial procedures set forth in protocols, differences in the size and type of the patient populations, changes in and adherence to the dosing regimen and other clinical trial protocolsprotocols, and the rate of dropout among clinical trial patients. Any Phase 2 or 3 trial results may not be representative of Phase 1 results, and such Phase 2 or 3 trial results may not be accepted by the FDA as pivotal and sufficient for approval, and additional trials may be required to establish that our product candidates are safe and effective. Further, in our oncology clinical trials to date, we have used achievement of stable disease as evidence for disease control (stable disease, partial response or complete response) by our product candidates; however, the FDA does not view stable disease as an objective response for the purposes of FDA approval. If we fail to receive positive results in clinical trials of our product candidates, the development timeline and regulatory approval and commercialization prospects for our most advanced product candidates, and, correspondingly, our business and financial prospects would be negatively impacted.

From time to time, we have publicly disclosed, and in the future willmay disclose, interim, top-line, or preliminary data from our preclinical studies and clinical trials, which are based on preliminary analyses of then-available data, and the results and related findings and conclusions are subject to change following a more comprehensive review and/or maturation of the data related to the particular study or trial. We also make assumptions, estimations, calculations, and conclusions as part of our analyses of data, and we may not have received or had the opportunity to fully and carefully evaluate all data. Therefore, final results from the studies may differ from the top-line results initially reported, and the final results may indicate different conclusions once additional data have been evaluated. As such, top-line data should be viewed with caution until the final data are available. In addition, the information we choose to publicly disclose regarding a particular study or clinical trial is based on what is typically extensive data, and you or others may not agree with what we determine is material or otherwise appropriate information to include in our disclosure. If the final results differ from the interim, top-line, or preliminary data, or if others, including regulatory authorities, disagree with the conclusions reached, our ability to obtain approval for, and to commercialize, our product candidates may be harmed, which may negatively affect our business, financial condition, results of operations, and prospects. Further, disclosure of interim data by us or by our competitors could result in volatility in the price of our common stock.

The market may not be receptive to our product candidates based on a novel therapeutic modality,candidates, and we may not generate any future revenue from the sale or licensing of product candidates.

Even if regulatory approval is obtained for a product candidate, we may not generate or sustain revenue from sales of the product due to factors such as whether the product can be sold at a competitive cost, competition in the therapeutic area(s) we have received or may receive approval for,approval, and whether it will otherwise be accepted in the market. Historically, there have been concerns regarding the safety and efficacy of ADCs, and an ADC drug was voluntarily withdrawn from the market for an extended period of time.time, although it has since been re-approved by the FDA. These historical concerns may negatively impact the perception market participants have on ADCs, including our product candidates.candidates, though advances in ADC technology have ameliorated these concerns to some degree. Additionally, the product candidates that we are developing are based on our proprietary XpressCF® and XpressCF+® platforms, which are new technologies. Market participants with significant influence over acceptance of new treatments, such as physicians and third-party payors, may not adopt an ADC product, or a product or treatment based on our novel cell-free production technologies, and the medical community and third-party payors may not be compelled to accept and use, or to provide favorable reimbursement for, any product candidates developed by us or our existing or future collaborators. Market acceptance of our product candidates will depend on the following, among other factors:

iADCDual-payload andADC ADC2technology areis novel technologies,novel, which makes it difficult to predict the time, risks and cost of development and of subsequently obtaining regulatory approval of these potential product candidates.

Certain of our preclinical product candidates are based on our proprietary iADC and ADC2 technology. Some of ourOur future success dependsdepends, in part, on the successful development of thisour proprietary dual-payload ADC technology and products basedderived onfrom it. To our knowledge, no regulatory authority has granted approval to any person or entity, including us, to market and commercialize therapeutics using any dual-payload ADC technology, including our novel anddual-payload unprecedented iADC or ADC2ADC technology. We may never receive approval to market and commercialize any potential iADCdual-payload or ADC2ADC product candidate.

If we uncover any previously unknown risks related to our iADCdual-payload and ADC2ADC technology, or if we experience unanticipated or unsolvable problems or delays in developing our iADCdual-payload or ADC2ADC product candidates, we may be unable to complete our preclinical studies and clinical trials, meet the obligations of our collaboration and license agreements, or commercialize our product candidates on a timely or profitable basis. Alternatively, we may be required to make amendments to our trial protocol, which could result in additional costs and may also delay our anticipated clinical development timelines. If serious adverse events or unacceptable side effects are observed in preclinical studies or clinical trials of a product candidate based on our iADCdual-payload or ADC2ADC technology, or if iADCsdual-payload or ADC2sADCs were shown to have limited efficacy, our ability to develop other product candidates based on our iADCdual-payload or ADC2ADC technology would be adversely affected.

Since 2014, we have entered into several collaborations to develop and commercialize certain cancer and other therapeutics. Our XpressCF® and XpressCF+® platforms have also supported a spin-out company, now known as Vaxcyte Inc., focused on discovery and development of vaccines for the treatment and prophylaxis of infectious disease. In addition, we may in the future seek third-party collaborators for research, development and commercialization of other therapeutic technologies or product candidates. Biopharmaceutical companies arehave been, and will likely continue to be, our priorprincipal and likely future collaboratorspartners for any marketing, distribution, development, licensing orand broader collaboration arrangements. With respect toUnder our existing collaboration agreements, and what we expect will be the case withexpect, any future collaboration agreements, weour have and would expectability to have limited control overinfluence the amount and timing of resources that our collaborators dedicate to the development or commercialization of our product candidates.candidates is, and will likely remain, limited. Moreover, our ability to generate revenues from these arrangements will depend on our collaborators’ abilities to successfully perform the functions assigned to them in these arrangements.

collaborators may not pursue development and commercialization of our product candidates or may elect not to continue or renew development or commercialization programs based on preclinical studies or clinical trial results, changes in the collaborators’ strategic focus or available funding, or other external factors such as an acquisition that diverts resources or creates competing priorities;

Our existing collaborations with Astellas, Ipsen, VaxcyteAstellas and TaslyVaxcyte are important to our business. If our collaborators cease development efforts under our existing or future collaboration agreements, fail to fulfill their contract obligations, or if any of those agreements are terminated, these collaborations may fail to lead to commercial products and we may never receive milestone payments or future royalties under these agreements.

We have entered into collaborations with other biotechnology companies to develop or commercialize several of our product candidates, and such collaborations currently represent a significant portion of our product pipeline and discovery and preclinical programs. A substantial portion of our revenue to date has been derived from our collaborations, and a significant portion of our future revenue and cash resources is expected to be derived from some of these agreements, along with our royalty monetization agreement, or Purchase Agreement, with an affiliate of Blackstone Life Sciences, or Blackstone, or other similar agreements into which we may enter in the future. Revenue from research and development collaborations depends upon continuation of the collaborations, payments for research and development and other services and product supply, and the achievement of milestones, contingent payments and royalties, if any, derived from future products developed from our research. If we are unable to successfully advance the development of our product candidates, achieve milestones or earn contingent payments under our collaboration agreements or royalty monetization agreement, future revenue and cash resources will be substantially less than expected.

We are unable to predict the success of our collaborations and we may not realize the anticipated benefits of our strategic collaborations. Our collaborators have discretion in determining and directing the efforts and resources, including the ability to discontinue all efforts and resources, they apply to the development and, if approval is obtained, commercialization and marketing of the product candidates covered by such collaborations. As a result, our collaborators may elect to de-prioritize our programs, change their strategic focus or pursue alternative technologies in a manner that results in reduced, delayed or no revenue to us. For example, each of EMD Serono, BMSBMS, Merck and MerckIpsen elected not to continue the development of their licensed product candidates, and our existing collaborator, Astellas, decided not to nominate a third program under our collaboration; each such decision was noted as based on strategic portfolio considerations. Our collaborators may have other marketed products and product candidates under collaboration with other companies, including some of our competitors, and their corporate objectives may not be consistent with our best interests. Our collaborators may also be unsuccessful in developing or commercializing our products. If our collaborations are unsuccessful, our business, financial condition, results of operations and prospects could be adversely affected. Our collaborators may fail to live up to the terms of their agreements with us, which would require us to seek to enforce our agreements in accordance with the dispute resolution procedures set forth therein.in such agreements. These procedures may require us to engage in litigation or arbitration to enforce our rights, which can be expensive, time-consuming and distracting to our management and Board of Directors. Further, the type and timing of resolution of such disputes are difficult to predict; and there is the potential that we could fail to enforce our rights either in partwhole or in whole.part. Lastly, even if we successfully enforce our rights under our agreements with our collaborators, there is the possibility that we could fail to recover our expectancy following the litigation or arbitration, particularly for collaborators that are not subject to the jurisdiction of U.S. courts.

Before we may initiate a clinical trial or commercialize any of our product candidates, we must demonstrate to the FDA that the chemistry, manufacturing and controls for our product candidates meet applicable requirements, and in the European Union, or EU, a manufacturing authorization must be obtained from the appropriate EU regulatory authorities. The FDA has allowed clinicalour trial use of ourcell-free product candidatescandidates, and others of our or our partners’ product candidatescandidates, to proceed through clinical trials; however, because no product manufactured on a cell-free manufacturing platform has yet been approved in the United States, there is no manufacturing facility that has demonstrated the ability to comply with FDA requirements for later stage clinical development or commercialization, and, therefore, the time frametimeframe for demonstrating compliance to the FDA’s satisfaction is uncertain. DelaysDespite incompleted establishingtechnology thattransfers to our contract manufacturing processorganization, andwe facilitycould complystill withexperience cGMPsunexpected or disruptionsunplanned insupply ourchain manufacturingissues processes, implementation of novel in-house technologies or scale-up activities,that may delay or disrupt our development efforts.

We have ongoingconducted technology transfers to enable large scale manufacture of extract and the reagents necessary to manufacture our products using our XpressCF® and XpressCF+® platforms.platforms and are likely to conduct additional similar technology transfers in the future. These large-scale technology transfers may fail or be delayed, resulting in impacts to our development timelines and the costs associated with manufacturing our development products.

OurWe inabilityexpect to rely on third parties to manufacture our drug supplies. If those third-parties are unable to manufacture sufficient quantities of our product candidates, or thewe losslose of our third-partysuch suppliers, or ourthey or their failurefail to comply with applicable regulatory requirements or to supply sufficient quantities at acceptable quality levels or prices, or at all, our business would be materially and adversely affect our business.affected.

We are ana clinical stage oncology company developing site-specific and novel-format antibody drug conjugates, or ADCs, enabled by our proprietary integrated cell-free protein synthesis platform, XpressCF®, and our site-specific conjugation platform, XpressCF+®. We aim to design and develop therapeutics using the most relevant and potent modalities, including ADCs, bispecific ADCs, immunostimulatory ADCs, or iADCs, and dual conjugatedual-payload ADCs, or ADC2s.dpADCs. Our molecules are directed primarily against clinically validated targets where the current standard of care is suboptimal. We believe that our platform allows us to accelerate the discovery and development of potential first-in-class and/or best-in-class molecules by enabling the rapid and systematic evaluation of protein structure-activity relationships to create optimized homogeneous product candidates. Our mission is to transform the lives of patients by creating medicines with improved therapeutic profiles for areas of unmet need.

Our highest priority wholly-owned preclinical product candidate is STRO-004. This product candidate isSTRO-004, a single homogeneous ADC directed against tissue factor, or TF, which we intendare to developdeveloping for the treatment of solid tumors. We anticipatebelieve filingSTRO-004 has the potential to be a best-in-class ADC targeting TF. In preclinical studies, STRO-004 has demonstrated potent antitumor activity and the potential for a differentiated safety profile. We filed an IND and received IND clearance for STRO-004 in theOctober second2025, halfand ofinitiated a Phase 1 trial in November 2025.

Our preclinical assets include STRO-0227 and STRO-006. STRO-006 is an ADC targeting Integrinß6, or ITGß6. We believe STRO-004STRO-006 has the potential to be a best-in-class ADC targeting TF.ITGß6 Preclinicalbased dataon suggestpreclinical studies that STRO-004have hasdemonstrated potent antitumor activity and the potential for a differentiated safety profile. OurIND-enabling otheractivities preclinicalare assetsunderway includefor STRO-006 that could potentially support an ADCIND targetingfiling Integrinβ6in andconnection ADC2s,with andthis iADCs.program Wein plan to file three INDs over the next three years, including for STRO-004.2026.

Our XpressCF® and XpressCF+® platforms have also supported Vaxcyte, focused on discovery and development of vaccines for the treatment and prophylaxis of infectious disease. The lead programs for Vaxcyte are VAX-31 and VAX-24, its 31-valent and 24-valent, respectively, pneumococcal conjugate vaccine candidates. Vaxcyte is responsible for performing all research and development activities,activities and we provide technical support and supply XtractCF® and other materials to Vaxcyte.support. In June 2023, we entered into a purchase and sale agreement, or the Purchase Agreement with Blackstone, in which Blackstone acquired the right to receive our 4% royalty, or revenue interest, in the potential future net sales of Vaxcyte products, including Vaxcyte’s pneumococcal conjugate vaccine, or PCV, products, such as VAX-24 and VAX-31. Following agreement with Vaxcyte on the Form Definitive Agreement and upon effectiveness of an amendment to the licensing agreement, the revenue interest in the 4% royalty on potential future sales of Vaxcyte products other than Vaxcyte’s PCV products reverted to us. Thus, we retain the right to receive a 4% royalty on sales of Vaxcyte’s products other than PCV products. In November 2023, Vaxcyte exercised its option to access expanded rights to develop and manufacture cell-free extract for use in development and manufacture of its vaccine products, among certain other rights.

Since the commencement of our operations, we have devoted substantially all of our resources to performing research and development and manufacturing activities in support of our own product development efforts and those of our collaborators, raising capital to support and expand such activities and providing general and administrative support for these operations. We have funded our operations to date primarily from upfront, milestone and other payments under our collaboration agreements with BMS, Merck, Astellas, Vaxcyte, Ipsen, EMD Serono, BioNova, and Tasly, the issuance and sale of redeemable convertible preferred stock, our initial public offering, or IPO, follow-on public and other offerings of common stock, sales of our common stock through our At-the-Market Facility (“ATM Facility”) pursuant to our Open Market Sales AgreementSM dated April 2, 20212021, (or the “Sales Agreement”)Agreement, with Jefferies LLCLLC, (“Jefferies”),or Jefferies, debt financing, sale of our holdings of Vaxcyte common stock, and the royalty monetization agreement with Blackstone.

We do not have any products approved for commercial sale and have not generated any revenue from commercial product sales. We had a loss from operations of $158.4 million and a net loss of $191.1 million for the year ended December 31, 2025. We had a loss from operations of $238.5 million and a net loss of $227.5 million for the year ended December 31, 2024,million, which net loss included the non-operating, realized gain of $32.1 million related to the sale of our holdings of Vaxcyte common stock. We had a loss from operations of $89.3 million and net loss of $106.8 million, which net loss included the non-operating, unrealized gain of $9.9 million related to our holdings of Vaxcyte common stock, for the year ended December 31, 2023.2024. Substantially all of our losses have resulted from expenses incurred in connection with our research and development programs and from general and administrative costs associated with our operations. We cannot assure you that we will have net income or that we will generate positive cash flow from operating activities in the future. As of December 31, 2024,2025, we had an accumulated deficit of $786.9$978.0 million. We do not expect to generate any revenue from commercial product sales unless and until we successfully complete development and obtain regulatory approval for one or more of our product candidates, which we expect will take a number of years. If we obtain regulatory approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, access, marketing, manufacturing and distribution. We expect a short-term reduction in operating expenses as we strategically reprioritize our resources. However, over the long term, we anticipate an increase in our operating expenses would increase as we advance our product candidates through clinical development, seek regulatory approvals for our product candidates, engage in other research and development activities, expand our pipeline of product candidates, maintain and expand our intellectual property portfolio, seek regulatory and marketing approval for any product candidates that we may develop, acquire or in-license other assets or technologies, ultimately establish a sales, marketing and distribution infrastructure to commercialize any products for which we may obtain marketing approval, and operate as a public company. In light of our current resources and the cost of development, we are continuing our process of evaluating our programs and spending. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our clinical trials, our expenditures on other research and development activitiesand general and administrative activities, and the timing of achievement and receipt of upfront, milestones and other collaboration agreement payments.

We do not have any products approved for commercial sale and have not generated any revenue from commercial product sales. Our total revenue to date has been generated principally from our collaboration and license agreements with BMS, Merck, Astellas, Vaxcyte, Ipsen, EMD Serono, BioNova, and Tasly,other collaborators, and to a lesser extent, from manufacturing, supply and services and materials we provide to the above collaborators.

Research and development expense increaseddecreased by $71.6$85.6 million, or 40%,34%, during the year ended December 31, 20242025 as compared to the year ended December 31, 2023.2024. The overall increasedecrease was due primarily to increasesdecreases of $43.0$27.1 million in outside servicesservices, mainly due to increased CMO-related activities, $12.1$28.5 million in preclinical research and clinical development expenses, $11.3$19.3 million in personnel-related expenses, $5.6 million in laboratory supplies, $4.9 million in allocated facilities expenses and IT-related expenses, $4.3 million in personnel-related expenses due to higher headcount, $2.5 million in equipment and office-related expenses, and $0.2$0.3 million in travel-related expenses,expenses. partiallyFollowing offsetthe by a decreaseimplementation of $1.7the millionRestructuring Plans, we began reporting restructuring costs and other costs associated with the deprioritized luvelta program under "Restructuring and related costs" in laboratoryour supplies.financial statements.

General and administrative expense decreased by $14.1$7.4 million, or 23%,15%, during the year ended December 31, 20242025 as compared to the year ended December 31, 2023.2024. The overall decrease was due primarily to decreases of $10.5 million in IT-related expenses and $5.7$5.9 million in personnel-related expenses, partially offset by increases of $0.8$2.3 million in outside services, $0.6$0.5 million in equipment and office-related expenses, and $0.6$0.4 million in travel-related expenses, partially offset by an increase of $1.6 million in allocated facilities-relatedfacilities and IT-related expenses. Some general and administrative expenses previously recorded under this category are now reported under "Restructuring and related costs" in our financial statements following the implementation of our Restructuring Plans.

Interest income increaseddecreased by $4.1$9.4 million during the year ended December 31, 20242025 as compared to the year ended December 31, 2023,2024, due primarily to higherlower average investment balances and lower average rates of return in 2024.2025.

Interest and other income (expense), net, decreased by $37.0$29.6 million during the year ended December 31, 2024,2025, as compared to the year ended December 31, 2023,2024, due primarily to a recognized gain of $32.1 million gain on the sale of Vaxcyte common stock recognized during the year ended December 31, 2024 and decreasesa of $3.6$0.5 million decrease from foreign exchange fluctuations, partially offset by a $3.0 million decrease from the financing component related to the Astellas Agreement and $1.3 million in interest incurred on our loan which was fully paid in March 2024.Agreement.

During the year ended December 31, 2024, we sold the remaining 667,780 shares of Vaxcyte common stock for net proceeds of $74.0 million. As of December 31, 2025 and 2024, we do not hold any shares of Vaxcyte common stock.

In consideration for the rights and licenses granted by us to Ipsen in the Ipsen License Agreement, Ipsen (i) Ipsen paid us an upfront license fee in the amount of $50.0 million in April 2024 and (ii) Ipsen Biopharmaceuticals, Inc. (USA) (“Ipsen USA”) purchased 4,827,373482,738 shares of our common stock for $25.0 million, at a price of approximately $5.18$51.79 per share, in accordance with the terms set forth in a certain investment agreement by and between us and the Ipsen USA dated March 29, 2024 (the “Ipsen Investment Agreement”, and, together with the Ipsen License Agreement, the “Ipsen Agreements”).

Based upon our current operating plan, we believe that our existing capital resources as well as the proceeds from the February 2026 Offering will enable us to fund our operating expenses and capital expenditure requirements through at least the next twelve months after the date of this filing. We have based this estimate on assumptions that may prove to be wrong, and we could utilize our available capital resources sooner than we currently expect. We will continue to require additional financing to advance our current product candidates into and through clinical development, to develop, acquire or in-license other potential product candidates, pay our obligations and to fund operations for the foreseeable future.

In March 2025, we approved a restructuring plan with an associated reduction in workforce as a result of a review of current strategic priorities, resource allocation, and cost reduction intended to reduce operating costs, streamline operations and extend our cash runway. We intend to decommission or otherwise exit our manufacturing facility in San Carlos by the end of 2025mid-2026 and rely on an external manufacturing strategy where all elements of our product candidates and platform reagents are manufactured by qualified third-party CMOs.

Cash provided by investing activities of $218.5$45.0 million for the year ended December 31, 20242025 was primarily related to maturities and sales of marketable securities of $609.1 million, and net proceeds from the sale of Vaxcyte common stock of $74.0$311.7 million, partially offset by purchases of marketable securities of $461.5$265.0 million, and purchases of property and equipment of $3.1$1.7 million, principally for laboratory equipment.

As of December 31, 2024,2025, we had federal net operating loss, or NOL, carryforwards of $149.8$376.3 million and federal general business credits from research and development expenses totaling $30.5$35.9 million, as well as state NOL carryforwards of $108.0$108.2 million and state research and development credits of $32.1$33.6 million.Ifmillion. If not utilized, the federal NOL carryforwards will expire at various dates beginning in 2027, and the federal credits will expire at various dates beginning in 2032. The state NOL carryforwards will expire at various dates beginning in 2030, if not utilized. The state research and development tax credits can be carried forward indefinitely.

To date, we have no products approved for commercial sale, have not generated any revenue from commercial product sales and, as of MarchJune 31,30, 2026, had an accumulated deficit of $1,016.4$1,055.0 million. For the threesix months ended MarchJune 31,30, 2026 and the year ended December 31, 2025, our net loss was $38.5$77.0 million and $191.1 million, respectively. Substantially all of our losses have resulted from expenses incurred in connection with our research and development programs and from general and administrative costs associated with our operations. In addition, our expenses could increase beyond expectations if we are required by the FDA, or foreign regulatory agencies, to perform studies or clinical trials in addition to those studies and clinical trials that we currently anticipate conducting for our product candidates, or if there are any delays in our or our partners completing clinical trials or the development of any of our product candidates. Our technologies and product candidates are in varying stages of development, and we are subject to the risks of failure inherent in the development of product candidates based on novel technologies. In addition, we have not yet demonstrated an ability to successfully overcome many of the risks and uncertainties frequently encountered by companies in new and rapidly evolving fields, particularly in the biotechnology industry. Furthermore, we do not expect to generate any revenue from commercial product sales for the foreseeable future, and we expect to continue to incur significant operating losses for the foreseeable future due to the cost of research and development, preclinical studies and clinical trials and the regulatory approval process for our product candidates and manufacturing clinical and early commercial supply of our product candidates. We expect our net losses to increase substantially as we progress further into development of our lead programs and create additional infrastructure to support operations as a public company. However, the amount of our future losses is uncertain. We may never generate revenues from the commercial sale of our or our collaborators’ products. Our ability to achieve profitability, if ever, will depend on, among other things, our, or our existing or future collaborators’, successful development of product candidates, evaluating the related commercial opportunities, obtaining regulatory approvals to market and commercialize product candidates, manufacturing any approved products on commercially reasonable terms, establishing a sales and marketing organization or suitable third-party alternatives for any approved product, and raising sufficient funds to finance business activities. If we, or our existing or future collaborators, are unable to develop our technologies and commercialize one or more of our product candidates or if sales revenue from any product candidate that receives approval is insufficient, we will not achieve profitability, which could have a material and adverse effect on our business, financial condition, results of operations and prospects. Even if we achieve profitability in the future, we may not be able to sustain profitability in subsequent periods.

Since our inception, we have invested a significant portion of our efforts and financial resources in research and development activities for our preclinical and clinical-stage product candidates and the development of our technology platform. Preclinical studies and clinical trials for our product candidates have required substantial funds to date and will continue to require substantial funds to complete. As of MarchJune 31,30, 2026, we had $202.6$164.3 million in cash, cash equivalents and marketable securities. We expect to incur substantial expenditures in the foreseeable future as we seek to advance multiple product candidates through clinical development, manufacturing, the regulatory approval process and, if approved, commercial launch activities, as well as in connection with the continued development of our technology platform. Based on our current operating plan, we believe that our available cash, cash equivalents and marketable securities will be sufficient to fund our operations through at least the next 12 months. However, our future capital requirements and the period for which we expect our existing resources to support our operations may vary significantly from what we expect, and we may need to seek additional funds sooner than planned. Our monthly spending levels vary based on new and ongoing research and development and other corporate activities. Because the length of time and activities associated with successful research and development of our product candidates is highly uncertain, we are unable to estimate the actual funds we will require for development and any marketing and commercialization activities for approved products. For example, the timing and amount of our operating expenditures will depend largely on:

Our business is dependent on the success of our product candidates, including STRO-004, STRO-006 and STRO-227, which are generated from our proprietary XpressCF® and XpressCF+® platforms. Existing and future preclinical studies and clinical trials of our product candidates may not be successful. If we are unable to commercialize our product candidates or experience significant delays in doing so, our business will be materially harmed.

We have invested a significant portion of our efforts and financial resources in the development of our proprietary XpressCF® and XpressCF+® platforms and our proprietary product candidates, including STRO-004, STRO-006 and STRO-227. Our ability to generate commercial product revenues, which we do not expect will occur for many years, if ever, will depend heavily on the successful development and eventual commercialization of our product candidates. We have not previously submitted a new drug application, or NDA, or a biologics license application, or BLA, to the FDA, or similar regulatory approval filings to comparable foreign authorities, for any product candidate, and we cannot be certain that our product candidates will be successful in clinical trials or receive regulatory approval. Further, our product candidates may not receive regulatory approval even if they are successful in clinical trials. If we do not receive regulatory approvals for our product candidates, we may not be able to continue our operations. Even if we successfully obtain regulatory approvals to market our product candidates, our revenues will be dependent, in part, upon the size of the markets in the territories for which we gain regulatory approval and have commercial rights. Our revenue may also be dependent, in part, on any third-party collaborator’s ability to co-commercialize such product candidate or to commercialize any companion diagnostic for such product candidate, as applicable. If the markets for patient subsets that we are targeting are not as significant as we estimate, we may not generate significant revenues from sales of such products, if approved.

We are developing a pipeline of product candidates using our proprietary XpressCF® and XpressCF+® platforms. We believe that product candidates identified with our product discovery platform may offer an improved therapeutic approach by taking advantage of precision design and rapid empirical optimization, thereby reducing the dose-limiting toxic effects associated with existing products. However, the scientific research that forms the basis of our efforts to develop product candidates based on our XpressCF® and XpressCF+® platforms is ongoing. Further, the scientific evidence to support the feasibility of developing therapeutic treatments based on our XpressCF® and XpressCF+® platforms is both preliminary and limited.

Our current and prior product candidates have been tested in a relatively limited number of clinical trial patients. We may ultimately discover that our XpressCF® and XpressCF+® platforms and any product candidates resulting therefrom do not possess certain properties required for therapeutic effectiveness. XpressCF® and XpressCF+® product candidates may also be unable to remain stable in the human body for the period of time required for the drug to reach the target tissue or they may trigger immune responses that inhibit the ability of the product candidate to reach the target tissue or that cause adverse side effects in humans. We currently have only limited data, and no conclusive evidence, to suggest that we can introduce these necessary properties into these product candidates derived from our XpressCF® and XpressCF+® platforms. We may spend substantial funds attempting to introduce these properties and may never succeed in doing so. In addition, product candidates based on our XpressCF® and XpressCF+® platforms may demonstrate different chemical and pharmacological properties in patients than they do in laboratory studies. Although our XpressCF® and XpressCF+® platforms and certain product candidates have produced successful results in animal studies, they may not demonstrate the same chemical and pharmacological properties in humans and may interact with human biological systems in unforeseen, ineffective or harmful ways. These unknowns and other emerging findings from our clinical trials and preclinical studies may result in protocol amendments, which may result in additional costs and may also delay our anticipated clinical timelines.

If product candidates based on our XpressCF® and XpressCF+® platforms are unable to demonstrate sufficient safety and efficacy data to obtain marketing approval, we may never succeed in developing a marketable product, we may not become profitable, and the value of our common stock will decline. The regulatory approval process for novel product candidates such as ours can be more expensive and take longer than for other, better known or extensively studied product candidates. We are not aware of any company currently developing a therapeutic using our approach to ADC or dual-payload ADC development, and no regulatory authority has granted approval for such a therapeutic. We believe the FDA has limited experience with therapeutics in oncology or other disease areas developed in cell-free-based synthesis systems, which may increase the complexity, uncertainty and length of the regulatory approval process for our product candidates. For example, our product candidates contain cleavable or non-cleavable linker-payload combinations or novel payloads that may result in unforeseen events when administered in a human. We and our existing or future collaborators may never receive approval to market and commercialize any product candidate. Even if we or an existing or future collaborator obtains regulatory approval, the approval may be for targets, disease indications or patient populations that are not as broad as we intended or desired or may require labeling that includes significant use or distribution restrictions or safety warnings. We or an existing or future collaborator may be required to perform additional or unanticipated clinical trials to obtain approval or be subject to post-marketing testing requirements to maintain regulatory approval. If the products resulting from our XpressCF® and XpressCF+® platforms prove to be ineffective, unsafe or commercially unviable, our platforms and pipeline would have little, if any, value, which would have a material and adverse effect on our business, financial condition, results of operations and prospects.

We have entered, and may in the future seek to enter, into collaborations with third parties for the development and commercialization of our product candidates using our XpressCF® and XpressCF+® platforms. If we fail to enter into such collaborations, or such collaborations are not successful, we may not be able to capitalize on the market potential of our XpressCF® and XpressCF+® platforms and resulting product candidates.

Since 2014, we have entered into several collaborations to develop and commercialize certain cancer and other therapeutics. Our XpressCF® and XpressCF+® platforms have also supported a spin-out company, now known as Vaxcyte Inc., focused on discovery and development of vaccines for the treatment and prophylaxis of infectious disease. In addition, we may in the future seek third-party collaborators for research, development and commercialization of other therapeutic technologies or product candidates. Biopharmaceutical companies have been, and will likely continue to be, our principal partners for marketing, distribution, development, licensing and broader collaboration arrangements. Under our existing collaboration agreements, and we expect, any future collaboration agreements, our ability to influence the amount and timing of resources that our collaborators dedicate to the development or commercialization of our product candidates is, and will likely remain, limited. Moreover, our ability to generate revenues from these arrangements will depend on our collaborators’ abilities to successfully perform the functions assigned to them in these arrangements.

We have entered into collaborations with other biotechnology companies to develop or commercialize several of our product candidates, and such collaborations currently represent a significant portion of our product pipeline and discovery and preclinical programs. A substantial portion of our revenue to date has been derived from our collaborations, and a significant portion of our future revenue and cash resources is expected to be derived from some of these agreements, along with our royalty monetization agreement, or Purchase Agreement, with an affiliate of Blackstone Life Sciences, or Blackstone, or other similar agreements into which we may enter in the future. Revenue from research and development collaborations depends upon continuation of the collaborations, payments for research and development and other services and product supply, and the achievement of milestones, contingent payments and royalties, if any, derived from future products developed from our research. If we are unable to successfully advance the development of our product candidates, achieve milestones or earn contingent payments under our collaboration agreements or royalty monetization agreement, future revenue and cash resources will be substantially less than expected.

To date, no product developed on a cell-free manufacturing platform has received approval from the FDA, so the requirements for the manufacturing of products using our XpressCF® and XpressCF+® platforms are uncertain.

We have conducted technology transfers to enable large scalelarge-scale manufacture of extract and the reagents necessary to manufacture our products using our XpressCF® and XpressCF+® platforms and are likely to conduct additional similar technology transfers in the future. These large-scale technology transfers may fail or be delayed, resulting in impacts to our development timelines and the costs associated with manufacturing our development products.

In addition, there are risks associated with large scalelarge-scale manufacturing for clinical trials or commercial scale including, among others, cost overruns, potential problems with process scale-up, process reproducibility, stability issues, compliance with cGMPs and specifications, lot consistency, timely availability of raw materials and other technical challenges. We have previously, and may continue to, source certain of the raw materials needed for our product candidates from outside the United States. Although we have not experienced any material supply interruptions to date, it is possible that political, economic or public health events, including the ongoing conflict in Iran, could cause such interruptions in the future. Even if we or our collaborators obtain regulatory approval for any of our product candidates, there is no assurance that manufacturers will be able to manufacture the approved product to specifications acceptable to the FDA or other regulatory authorities, to produce it in sufficient quantities to meet the requirements for the potential launch of the product or to meet potential future demand. If our manufacturers are unable to produce sufficient quantities for clinical trials or for commercialization, commercialization efforts would be impaired, which would have an adverse effect on our business, financial condition, results of operations and prospects.

We may not be successful in our efforts to use our XpressCF® and XpressCF+® platforms to expand our pipeline of product candidates and develop marketable products.

We are aware of several companies that are developing ADCs, bispecific antibodies and cancer immunotherapies, including companies developing ADCs directed to the same targets as STRO-004, STRO-006 and STRO-227. For example, Pfizer has an approved ADC targeting TF, TIVDAK®, and is developing sigvotatug vedotin,vedotin anand ADCPF-08046876, two ADCs targeting Integrinβ6, alongside PF-08046876, another ITGB6-targeting ADC currently in pre-clinical development.ITGB6. In addition, large pharmaceutical companies and smaller biotechnology companies are developing other ADCs, including TF-targetingTF- and ITGB6-targeting ADCs; and we anticipate more TF-targeting ADCs, other potential TF-targeting modalities, and possibly more ITGB6-targeting therapeutics will be evaluated in the clinic in the coming years. Further, other companies may develop ADCs targeting receptors other than TF or ITGB6 for the treatment of the same indications for which we are developing STRO-004 and/or STRO-006. Moreover, we are aware of several companies that are also pursuing dual-payload ADCs for oncology indications, including some that have initiated clinical development and other companies that are clinically developing ADCs that target PTK7, the target of STRO-227. Many of these companies are well-capitalized and, unlike us, have significant clinical experience, and may include our existing or future collaborators. In addition, these companies compete with us in recruiting scientific and managerial talent.

As of MarchJune 31,30, 2026, we had 133128 full-time employees. As our development and commercialization plans and strategies develop, we expect to expand our employee base for managerial, operational, financial and other resources. In addition, we have limited experience in product development. As our product candidates enter and advance through preclinical studies and clinical trials, we will need to expand our development, regulatory and manufacturing capabilities or contract with other organizations to provide these capabilities for us. In the future, we expect to have to manage additional relationships with collaborators or partners, suppliers and other organizations. Our ability to manage our operations and future growth will require us to continue to improve our operational, financial and management controls, reporting systems and procedures. We may not be able to implement improvements to our management information and control systems in an efficient or timely manner and may discover deficiencies in existing systems and controls. Our inability to successfully manage our growth and expand our operations could have a material and adverse effect on our business, financial condition, results of operations and prospects.

We are increasingly dependent on information technology systems and infrastructure to operate our business. In the ordinary course of our business, we collect, use, store and transmit large amounts of confidential and sensitive information, including intellectual property, proprietary business information and personal information (including health related information). We have established physical, electronic and organizational measures designed to safeguard and secure our systems to prevent a security incident (which may include, for example, data breaches, viruses or other malicious code, coordinated attacks, data loss, phishingphishing, business email compromise, AI-generated impersonation, deepfake-enabled fraud, credential theft and other social engineering attacks, ransomware, distributed denial of service attacks, or other security or information technology incidents caused by threat actors, technological vulnerabilities or human error), and rely on commercially available systems, software, tools, and monitoring to provide security for our information technology systems and the processing, transmission and storage of information. We have also outsourced elements of our information technology infrastructure, and as a result, a number of third-party vendors have access to our information. Despite the implementation of security measures, our internal information technology systems and infrastructure, and those of our current and any future collaborators, CROs, CDMOs, third-party vendors, contractors and consultants and other third parties on which we rely, are vulnerable to breach, breakdown, damage from computer viruses, malware, natural disasters, terrorism, war, telecommunication and electrical failures, cyber-attacks or cyber-intrusions over the internet, attachments to emails, persons inside our organization, or persons with access to systems inside our organization.

We take steps designed to detect, mitigate, and remediate vulnerabilities in our information systems. We have not and may not in the future, however, detect and remediate all such vulnerabilities in our information technology systems, including on a timely basis, because such threats and techniques change frequently, are often sophisticated in nature, and may not be detected until after a security incident has occurred. Unremediated high risk or critical vulnerabilities pose material risks to our business that may be exploited and could result in a security incident. Further, we have experienced and may in the future experience delays in developing and deploying remedial measures designed to address any such identified vulnerabilities. In addition, as many of our employees work from home at least part of the time and utilize network connections outside our premises, including while at home, or in transit and in public locations, this poses increased risks to our information technology systems and data. Because AI-enabled attacks can evolve rapidly and adapt in response to defensive measures, our existing security controls, monitoring capabilities and employee awareness programs may not identify or prevent every attack before harm occurs.

In our ongoing efforts to innovate and optimize operational efficiency, we have integrated AI into various aspects of our workplace. For example, we have implemented AI machine learning for email behavioral monitoring. While AI presents opportunities for enhanced productivity and innovation, it also introduces inherent risks, including legal and regulatory, that could adversely impact our business and reputation. Proper use of AI can lead to improved decision-making, cost reduction, and competitive advantage. In addition, employees or third parties may unintentionally disclose confidential, proprietary or regulated information through the use of AI-enabled applications or services, or rely on inaccurate or manipulated AI-generated outputs in ways that adversely affect our operations, decision-making or compliance obligations. However, improper use, including algorithmic biases, ethical considerations, data privacy issues, unknown or zero-day software vulnerabilities, model poisoning, prompt injection, data leakage through AI services, unauthorized AI use ("shadow AI"), and compromise of AI-assisted business processes, and potential regulatory non-compliance, could result in reputational damage, legal liabilities, and financial losses. The rapidly evolving regulatory landscape surrounding AI also poses a risk, as new laws and regulations could impose additional compliance burdens, resulting in increased operational costs. We are committed to implementing robust governance and control mechanisms to mitigate these risks, but there can be no assurance that such measures will adequately prevent or mitigate the adverse effects that the integration and use of AI may have on our business, financial condition, and results of operations.

Our research, development and manufacturing involve the use of hazardous chemicals and materials, including radioactive materials. We maintain quantities of various flammable and toxic chemicals in our facilities that are required for our research, development and manufacturing activities. We generally contract with third parties for the disposal of these materials and wastes. We cannot eliminate the risk of contamination or injury from these materials. We and our third-party contractors are subject to federal, state and local laws and regulations governing the use, manufacture, storage, handling and disposal of these hazardous chemicals and materials. We believe our and our third-party contractors’ procedures for storing, handling and disposing these materials in our facilities comply with the relevant guidelines of the two municipalities, the county of San Mateo, the state of California and the Occupational Safety and Health Administration of the U.S. Department of Labor. Although we believe that our safety procedures for handling and disposing of these materials comply with the standards mandated by applicable regulations, including employee and contractor training and procedures regarding safe handling and disposal, the risk of accidental or mistaken contamination or injury from these materials cannot be eliminated. If an accident occurs, we could be held liable for resulting damages, which could be substantial and exceed any available insurance. We are also subject to numerous environmental, health and workplace safety laws and regulations, including those governing laboratory procedures, exposure to blood-borne pathogens and the handling of animals and biohazardous materials. Although we maintain workers’ compensation insurance to cover us for costs and expenses we may incur due to injuries to our employees resulting from the use of these materials or from other hazards potentially present in our workplaces, such as high voltage electricity, process steam or other hot material, liquid nitrogen or other cold material, materials stored under pressure, laboratory instruments that incorporate powerful lasers or magnets, sonic resonance, heavy machinery, and the like, this insurance may not provide adequate coverage against potential liabilities. While we maintain pollution legal liability insurance for our manufacturing facility in San Carlos, California, weWe do not maintain insurance for environmental liability or toxic tort claims that may be asserted against us in connection with our storage or disposal of biological or hazardous materials in our other locations. Additional federal, state and local laws and regulations affecting our operations may be adopted in the future and existing laws and regulations could become more stringent. Further, we may incur substantial costs to comply with, and substantial fines or penalties if we violate, any of these laws or regulations.

Our current operations are located in our facilities in South San Francisco and San Carlos,Francisco, California. Any unplanned event, such as earthquake, flood, fire, explosion, extreme weather condition, epidemic, pandemic or contagious disease, power shortage, telecommunication failure or other natural or man-made accidents or incidents that result in us being unable to fully utilize our facilities, or the manufacturing facilities of our third-party contract manufacturers, may have a material and adverse effect on our ability to operate our business, particularly on a daily basis, and have significant negative consequences on our financial and operating conditions. Loss of access to these facilities may result in increased costs, delays in the development of our product candidates or interruption of our business operations. Earthquakes, epidemics, pandemics or contagious diseases, or other natural disasters could further disrupt our operations, and have a material and adverse effect on our business, financial condition, results of operations and prospects. If a natural disaster, power outage, epidemics, pandemics or contagious disease, or other events occurred that prevented us from using all or a significant portion of our headquarters, that damaged critical infrastructure, such as our research or manufacturing facilities or the manufacturing facilities of our third-party contract manufacturers, or that otherwise disrupted operations, it may be difficult or, in certain cases, impossible, for us to continue our business for a substantial period of time. The disaster recovery and business continuity plans we have in place may prove inadequate in the event of a serious disaster or similar event. We may incur substantial expenses as a result of the limited nature of our disaster recovery and business continuity plans, which could have a material adverse effect on our business. As part of our risk management policy, we maintain insurance coverage at levels that we believe are appropriate for our business. However, in the event of an accident or incident at these facilities, we cannot assure you that the amounts of insurance will be sufficient to satisfy any damages and losses. In addition, the long-term effects of climate change on general economic conditions and the pharmaceutical industry in particular are unclear, and may heighten or intensify existing risk of natural disasters. If our facilities, or the manufacturing facilities of our third-party contract manufacturers, are unable to operate because of an accident or incident or for any other reason, even for a short period of time, any or all of our research and development programs may be harmed. Further, many of our employees conduct business outside of our leased or owned facilities and these locations may be subject to additional security risks outside of our control. Any business interruption could have a material and adverse effect on our business, financial condition, results of operations and prospects.

Therapeutics in oncology or other disease areas developed in cell-free-based synthesis systems are a relatively new scientific field. We have obtained grants and issuances of, and have obtained a license from a third party on an exclusive basis to, patents related to our proprietary XpressCF® and XpressCF+® platforms. The issued patents and pending patent applications in the United States and in key markets around the world that we own or license claim many different methods, compositions and processes relating to the discovery, development, manufacture and commercialization of antibody-drug conjugates and dual payload antibody-drug conjugates, or components thereof.

As the field of antibody-drug conjugate and dual payload antibody-drug conjugates therapeutics continues to mature, patent applications are being processed by national patent offices around the world. There is uncertainty about which patents will issue and, if they do, as to when, to whom, and with what claims. In addition, third parties may attempt to invalidate our intellectual property rights. Even if our rights are not directly challenged, disputes could lead to the weakening of our intellectual property rights. Our defense against any attempt by third parties to circumvent or invalidate our intellectual property rights could be costly to us, could require significant time and attention of our management and could have a material and adverse effect on our business, financial condition, results of operations and prospects or our ability to successfully compete.

Because the antibody-drug conjugate and dual payload antibody-drug conjugates therapeutics landscape is still evolving, it is difficult to conclusively assess our freedom to operate without infringing on third-party rights. There are numerous companies that have pending patent applications and issued patents broadly covering antibodies generally, covering antibodies directed against the same targets as, or targets similar to, those we are pursuing, or covering linkers and cytotoxic payloads similar to those that we are using in our product candidates. For example, we are aware of an issued patent, expected to expire in 2031, that relates to strained alkyne reagents that can be used as synthetic precursors for certain of our linker-payload. If any of these patents are valid and not yet expired when, and if, we receive marketing approval for a product incorporating these components, as applicable, we may need to seek a license to one or more of these patents, each of which may not be available on commercially reasonable terms or at all. Failure to receive a license to any of these patents, or other potentially relevant patents currently unknown to us, could delay commercialization of STRO-004, STRO-006, STRO-227 or any other product candidate. Our competitive position may suffer if patents issued to third parties or other third-party intellectual property rights cover our products or product candidates or elements thereof, or our manufacture or uses relevant to our development plans. In such cases, we may not be in a position to develop or commercialize products or product candidates until such patents expire or unless we successfully pursue litigation to nullify or invalidate the third-party intellectual property right concerned, or enter into a license agreement with the intellectual property right holder, if available on commercially reasonable terms. There may be issued patents of which we are not aware, held by third parties that, if found to be valid and enforceable, could be alleged to be infringed by our XpressCF® and XpressCF+® platforms and related technologies and product candidates. There also may be pending patent applications of which we are not aware that may result in issued patents, which could be alleged to be infringed by our XpressCF® and XpressCF+® platforms and related technologies and product candidates. If such an infringement claim should be brought and be successful, we may be required to pay substantial damages, including potentially treble damages and attorneys’ fees for willful infringement, and we may be forced to abandon our product candidates or seek a license from any patent holders. No assurances can be given that a license will be available on commercially reasonable terms, if at all.

variations in the level of expense related to the ongoing development of our XpressCF® and XpressCF+® platforms, our product candidates or future development programs;

We cannot predict what effect, if any, sales of our shares in the public market or the availability of shares for sale will have on the market price of our common stock. However, future sales of substantial amounts of our common stock in the public market, including shares issued upon exercise of outstanding options or warrants, or the perception that such sales may occur, could adversely affect the market price of our common stock. For example, we are party to a Sales Agreement with Jefferies,TD Cowen, pursuant to which, from time to time, we may offer and sell through JefferiesTD Cowen common stock pursuant to one or more “at the market” offerings. Sales of our common stock under the Sales Agreement could be subject to business, economic or competitive uncertainties and contingencies, many of which may be beyond our control, and which could cause actual results from the sale of our common stock to differ materially from expectations. Any future sales of common stock through our “at the market” offering program will result in dilution and may have a negative impact on the price of our common stock.

The Phase 1 open-label, multicenter trial of STRO-004 is designed to evaluate the safety, pharmacokinetics, and preliminary anti-tumor activity of STRO-004 in patients with advanced TF-expressing solid tumors, including non-small cell lung cancer, head and neck squamous cell carcinoma, cervical cancer, colorectal cancer, pancreatic ductal adenocarcinoma, endometrial cancer, bladder cancer and bladdergastric/esophogeal cancer. The dose-escalation phase includes multiple cohorts with ascending dose levels, supported by strong tolerability in non-human primates at up to 50 mg/kg. DosingIn ofAugust patients2026, inwe thereported doseencouraging levelearly 2clinical cohortactivity wasincluding completedconfirmed and dosingunconfirmed ofpartial patientsresponses inwith the dose level 3 cohort was initiated in February 2026. We expect to report initial preliminary data, includingfavorable safety and pharmacokineticpharmacokinetics data,(PK) from this trialobserved in mid-2026.ongoing Phase 1 trial, and that dose optimization continues between 4-5 mg/kg with the maximum tolerated dose yet to be defined.

Our preclinical assets include STRO-227 and STRO-006. STRO-006 is an ADC targeting Integrinß6, or ITGß6.ITGB6. We believe STRO-006 has the potential to be a best-in-class ADC targeting ITGß6ITGB6 based on preclinical studies that have demonstrated potent antitumor activity and the potential for a differentiated safety profile. IND-enablingWe activitiesexpect areto underwayinitiate fora STRO-006Phase that1 couldclinical potentially support an IND submissiontrial in connection with this programSTRO-006 in the third quarter of 2026.

STRO-227 is our first wholly-owned dual-payload ADC, targeting Protein Tyrosine Kinase 7, or PTK7. This approach incorporates two distinct cytotoxic payloads, oneMMAE that(DAR2) is designed to inhibit tubulin and anotherexatecan that(DAR8) is designed to inhibit topoisomerase.topoisomerase, enabling complementary mechanisms of action within a single molecule. We have initiated certain chemistry, manufacturing and controls, or CMC, related activities for the PTK7-targeting dual-payload ADC and anticipate submitting an IND in connection with this program in late 2026.

Enabled through our proprietary XpressCF® and XpressCF+® platforms, we have entered into multitarget, product-focused collaborations with leading pharmaceutical and biotechnology companies in the field of oncology and we may enter into additional such collaborations in the future. We have an ongoing multitarget iADC collaboration with Astellas Pharma Inc. for the development of iADC targets (the “Astellas Agreement”).targets. Clinical trials for the first iADC licensed pursuant to the Astellas Agreement were initiated in the first quarter of 2026 and we expect the second iADC collaboration program to enter the clinic by the end of 2026. In addition, we may partner or out-license our wholly-owned preclinical or clinical development programs depending on resource and capital availability.

Since the commencement of our operations, we have devoted substantially all of our resources to performing research and development and manufacturing activities in support of our own product development efforts and those of our collaborators, raising capital to support and expand such activities and providing general and administrative support for these operations. We have funded our operations to date primarily from upfront, milestone and other payments under our collaboration agreements with BMS, Merck, Astellas, Vaxcyte, Ipsen, EMD Serono, BioNova, and Tasly, the issuance and sale of redeemable convertible preferred stock, our initial public offering, or IPO, follow-on public and other offerings of common stock, sales of our common stock through our At-the-Market Facility pursuant to our Open Market Sales AgreementSM dated April 2, 2021,2021 with Jefferies LLC, which was terminated in March of 2026, our At-the-Market Facility pursuant to our Sales Agreement dated March 23, 2026, or the Sales Agreement, with JefferiesTD Securities (USA) LLC, or Jefferies,TD Cowen, debt financing, sale of our holdings of Vaxcyte common stock, and the royalty monetization agreement with Blackstone.

In March 2025, our Board of Directors approved a strategic portfolio review, or the March 2025 Restructuring Plan, with an associated planned reduction in our workforce, as a result of its review of current strategic priorities, resource allocation, and cost reduction intended to reduce operating costs, streamline operations and extend our cash runway. In connection with this March 2025 Restructuring Plan, we deprioritized further investment in our late stage clinical development product candidate, luveltamab tazevibulin, which development has been terminated, and refocused our activities on our clinical and preclinical pipeline, including STRO-004, STRO-227, and STRO-006. In addition, in 2025, we made the strategic decision to cease operations at our San Carlos manufacturing facility and rely on an external manufacturing strategy, in which all elements of our product candidates and platform reagents are manufactured by qualified third-party CMOs. We have identified a contract manufacturing organization,organizations, or CMO,CMOs, to serve as our strategic partner for the production of cell-free extract and have initiated and completed technology transfer to this CMO. Similarly, we have identified a CMO to produce custom reagents used in our cell-free productionproduction, and have initiated and completed this technology transfertransfers asto well.these CMOs. Given the success of these technology transfers, we wound down our manufacturing activities in our San Carlos facility at the end of 2025 and expectcompleted tothe exit of the facility completely in 2026 upon expiration of our leases.

We do not have any products approved for commercial sale and have not generated any revenue from commercial product sales. We had a loss from operations of $29.7$59.5 million and a net loss of $38.5$77.0 million for the threesix months ended MarchJune 31,30, 2026. We had a loss from operations of $68.5$71.9 million and a net loss of $76.0$87.5 million for the threesix months ended MarchJune 31,30, 2025. Substantially all of our losses have resulted from expenses incurred in connection with our research and development programs and from general and administrative costs associated with our operations. We cannot assure you that we will have net income or that we will generate positive cash flow from operating activities in the future. As of MarchJune 31,30, 2026, we had an accumulated deficit of $1,016.4$1,055.0 million. We do not expect to generate any revenue from commercial product sales unless and until we successfully complete development and obtain regulatory approval for one or more of our product candidates, which we expect will take a number of years. If we obtain regulatory approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, access, marketing, manufacturing and distribution. We expect a reduction in operating expenses as we strategically reprioritize our resources. However, we anticipate our operating expenses would increase as we advance our product candidates through clinical development, seek regulatory approvals for our product candidates, engage in other research and development activities, expand our pipeline of product candidates, maintain and expand our intellectual property portfolio, seek regulatory and marketing approval for any product candidates that we may develop, acquire or in-license other assets or technologies, ultimately establish a sales, marketing and distribution infrastructure to commercialize any products for which we may obtain marketing approval, and operate as a public company. In light of our current resources and the cost of development, we are continuing our process of evaluating our programs and spending. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our clinical trials, our expenditures on other research and development and general and administrative activities, and the timing of achievement and receipt of upfront, milestones and other collaboration agreement payments.

The process of conducting the necessary preclinical and clinical research to obtain regulatory approval is costly and time consuming.time-consuming. The actual probability of success for our product candidates may be affected by a variety of factors including: the safety and efficacy of our product candidates, early clinical data, investment in our clinical programs, the ability of collaborators to successfully develop our licensed product candidates, competition, manufacturing capability and commercial viability. We may never succeed in achieving regulatory approval for any of our product candidates. As a result of the uncertainties discussed above, we are unable to determine the duration and completion costs of our research and development projects or when and to what extent we will generate revenue from the commercialization and sale of our product candidates.

Our general and administrative expenses consist primarily of personnel costs, expenses for outside professional services, including legal, human resources, audit, accounting and tax services and allocated facilities and IT-related costs. Personnel costs include salaries, employee benefits and stock-based compensation. We expect to incur expenses operating as a public company, including expenses related to compliance with the rules and regulations of the SEC and listing standards applicable to companies listed on the Nasdaq Global Market, additional insurance expenses, investor relations activities and other administrative and professional services. We expect a reduction in general and administrative expenses as we strategically reprioritize our resources. However, over the longer term, we anticipate such expenses would increase as we advance our product candidates through clinical development and toward potential commercialization.

In March 2025, we announced the March 2025 Restructuring Plan resulting in the prioritization of our three wholly-owned preclinical programs in our next-generation ADC pipeline. We also announced that we are deprioritizing additional investment into development of luvelta across all indications and are reducing headcount by nearly 50 percent. In September 2025, we announced a further reduction in our workforce of approximately one third of our remaining employees. In connection with these events, we reported clinical trial expenses and other third-party costs for the deprioritization of the luvelta program in "Restructuring and Related Costs" in our interim condensed Statements of Operations for the three months ended March 31, 2026.Operations.

Comparison of the Three Months Ended MarchJune 31,30, 2026, and 2025

Research and development expense decreased by $15.0$6.6 million, or 29%,17%, during the three months ended MarchJune 31,30, 2026, as compared to the three months ended MarchJune 31,30, 2025. The overall decrease was due primarily to decreases of $8.0$5.8 million in personnel-related expenses, $4.7 million in preclinical research and clinical development expenses, $3.5 million in laboratory supplies, $3.3$3.2 million in allocated facilities and IT-related expenses, and $2.1$2.7 million in outsidelaboratory services,supplies, and $0.2 million in equipment and office-related expenses, partially offset by ana $4.0 million increase ofin $6.9preclinical research and clinical development expenses and a $1.3 million increase in technologyoutside transfer expenses primarily driven by a $7.1 million charge related to a negotiated resolution associated with a pre‑existing technology transfer cost‑sharing arrangement.services. Following the implementation of the March 2025 Restructuring Plan, we began reporting restructuring costs and other costs associated with the deprioritized luvelta program under "Restructuring and related costs" in our interim condensed financial statements.

General and administrative expense decreased by $5.7$2.5 million, or 43%,24%, during the three months ended MarchJune 31,30, 2026, as compared to the three months ended MarchJune 31,30, 2025. The overall decrease was due primarily to decreases of $3.4$2.1 million in personnel-related expenses, $2.0$0.1 million in outside services, $0.2$0.1 million in allocated facilities and IT-related expenses, $0.1 million in travel-related expenses, and $0.1 million in travel-related expenses. Some generalequipment and administrativeoffice-related expenses previously recorded under this category are now reported under "Restructuring and related costs" in our interim condensed financial statements following the implementation of our Restructuring Plans.expenses.

Interest income decreased by $1.6$0.8 million during the three months ended MarchJune 31,30, 2026, as compared to the three months ended MarchJune 31,30, 2025, due primarily to lower average investment balances and lower average rates of return in 2026.

Non-cash interest expense increased by $0.1$0.2 million during the three months ended MarchJune 31,30, 2026, as compared to the three months ended MarchJune 31,30, 2025. Non-cash interest expense was recognized on our deferred royalty obligation related to the June 2023 sale of future Vaxcyte royalties pursuant to the Purchase Agreement, using the effective interest method based on the imputed interest rate derived from estimated amounts and timing of potential future royalty payments to be earned and received by Blackstone from Vaxcyte under the 2015 License Agreement.

Interest and other income (expense), net, decreased by $0.3$0.5 million during the three months ended MarchJune 31,30, 2026, as compared to the three months ended MarchJune 31,30, 2025, primarily due to the financing component related to the Astellas Agreement.

To date, we have incurred significant net losses, and negative cash flows from operations. Our operations have been funded primarily by payments received from our collaborators, and net proceeds from equity sales, debt, sale of shares of Vaxcyte common stock, and a royalty monetization. As of MarchJune 31,30, 2026, we had cash, cash equivalents and marketable securities of $202.6$164.3 million, and an accumulated deficit of $1,016.4$1,055.0 million.

In September 2020, we entered into a sublease agreement (the "Sublease”) with Five Prime Therapeutics, Inc. (the "Sublessor") for approximately 115,466 square feet, in a building located in South San Francisco, California (the "Premises"). We use the Premises as our corporate headquarters and to conduct (or expand) research and development activities. We commenced making monthly payments for the first 85,755 square feet of the Premises, or Initial Premises, in July 2021, with occupancy of such space commencing in August 2021. We were provided early access to the Initial Premises in the fourth quarter of 2020 to conduct certain planning and tenant improvement work. The Sublease is subordinate to the lease agreement, effective December 12, 2016, between the Sublessor and HCP Oyster Point III LLC (the "Landlord"). We commenced using the remaining 29,711 square feet of the Premises (the "Expansion Premises") on July 1, 2023 under the Sublease. The Sublease for both the Initial Premises and Expansion Premises will expire on December 31, 2027. With a commencement date on the Initial Premises of July 1, 2021, and Expansion Premises of July 1, 2023, the aggregate estimated base rent payments due over the term of the Sublease are approximately $40.4 million, including the approximately $5.2 million in potential financial benefit to us of base rent abatement to be provided by the Sublessor, subject to certain terms contained in the Sublease. The Sublease contains customary provisions requiring us to pay our pro rata share of utilities and a portion of the operating expenses and certain taxes, assessments and fees of the Premises and provisions allowing the Sublessor to terminate the Sublease upon the termination of the lease with the Landlord or if we fail to remedy a breach of certain of our obligations within specified time periods. Additionally, we posted a security deposit of $0.9 million, which is reflected as restricted cash in non-current assets on our Balance Sheets as of MarchJune 31,30, 2026 and December 31, 2025.

Cash used in operating activities for the threesix months ended MarchJune 31,30, 2026 was $42.3$80.5 million. Our net loss of $38.5$77.0 million included non-cash amounts of $9.5$19.3 million for non-cash interest expense on our deferred royalty obligation, $1.6$3.6 million for stock-based compensation, $1.3$2.5 million for depreciation and amortization, $1.2$2.4 million for non-cash lease expense, and $0.4$0.9 million for the accretion of discount on marketable securities. Cash used in operating activities also reflected a net change in operating assets and liabilities of $16.9$30.7 million, due to a decrease of $9.3$8.5 million in accrued compensation expense primarily due to bonuses paid in 2026 in connection with certain company 2025 goal achievements, an increase of $8.5 million in accounts receivable due primarily to the $10 million milestone payment to be received from Astellas, which was received in April 2026, a decrease of $2.5 million in accounts payable due to timing of payments, a decrease of $2.0 million in operating lease liabilities, a decrease of $2.0$6.1 million in deferred revenue resulting from revenue recognized under the Astellas Agreement, a decrease of $4.9 million in operating lease liabilities, a decrease of $4.6 million in accrued expenses and other liabilities due primarily to a payment made to Vaxcyte partially offset by an increase in technology transfer costs, a decrease of $4.2 million in accounts payable due to timing of payments, an increase of $1.8 million in accounts receivable, and an increase of $1.0$0.6 million in prepaid expenses and other assets due primarily to an increase in clinical trials activities for STRO-004, partially offset by an increase of $8.4 million in accrued expenses and other liabilities due primarily to an increase in technology transfer costs.STRO-004.

Cash used in operating activities for the threesix months ended MarchJune 31,30, 2025 was $67.9$112.6 million. Our net loss of $76.0$87.5 million included non-cash amounts of $9.3$19.0 million for non-cash interest expense on our deferred royalty obligation, $5.5$10.8 million for stock-based compensation, $1.9$3.8 million for depreciation and amortization, $1.4$2.8 million for non-cash lease expense, and $1.1$2.1 million for the accretion of discount on marketable securities. Cash used in operating activities also reflected a net change in operating assets and liabilities of $9.1$59.7 million, due to an increase of $4.9 million in accounts receivable primarily due to a $7.5 million receivable from Astellas for their initiation of an IND-enabling toxicology study for the first program in our collaboration with Astellas, which was partially offset by a decrease in accounts receivable from our other collaborators, a decrease of $4.7$63.4 million in deferred revenue primarilyresulting duefrom Ipsen's strategic decision not to revenueadvance recognizedthe STRO-003 program under theits Astellaspartnership Agreement,with us, a decrease of $1.7$5.7 million in ouraccounts payable due to timing of payments, a decrease of $3.6 million in operating lease liability,liabilities, and a decrease of $1.3$1.1 million in accrued compensation expense primarily due to bonuses paid in 2025 in connection with certain company 2024 goal achievements, which was partially offset by an increase in severance andpayments benefits obligationsmade under the Restructuring Plan. The decrease in operating assets and liabilities werePlan, partially offset by an increase of $3.7$7.1 million in accounts payable, accrued expenses and other liabilities due primarily to timingincreases in CMO restructuring costs as a result of payments.the deprioritization of luvelta, and a decrease of $6.4 million in prepaid expenses and other assets due to a decrease in clinical trials and CMO-related activities as a result of the deprioritization of STRO-002.

Cash used in investing activities of $45.3$25.9 million for the threesix months ended MarchJune 31,30, 2026 was primarily related to purchases of marketable securities of $124.7$152.6 million, partially offset by maturities of marketable securities of $76.2$108.2 million, and sales of marketable securities of $3.2$18.4 million.

Cash used in investing activities of $16.3$13.7 million for the threesix months ended MarchJune 31,30, 2025 was primarily related to purchases of marketable securities of $142.4$171.0 million, and purchases of property and equipment of $1.2$1.3 million, principally for laboratory equipment, partially offset by maturities of marketable securities of $135.7 million, and sales of marketable securities of $127.3$22.8 million.

Cash provided by financing activities of $103.1$102.7 million for the threesix months ended MarchJune 31,30, 2026 was primarily related to net proceeds from the sale of common stock in February 2026.

Cash provided by financing activities of $0.1 million for the threesix months ended MarchJune 31,30, 2025 was immaterial, primarily related to $0.3$0.2 million of net proceeds received from participants in our employee equity plans, partially offset by a $0.2 million tax payment related to the net shares settlement of vested restricted stock units.