SUTRO BIOPHARMA, INC.

Previous wording

We are an 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, and dual-payload ADCs, which include immunostimulatory ADCs, or iADCs. 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.

Current wording

We are a 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-payload ADCs, or 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.

Previous wording

Our most advanced preclinical stage programs are STRO-004 and STRO-006, with STRO-004 being our current highest priority wholly-owned product candidate. STRO-004 is a single homogeneous ADC directed against tissue factor, or TF, which we intend to develop for the treatment of solid tumors. We believe STRO-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 the fourth quarter of 2025, and plan to initiate clinical development by the end of 2025.

Current wording

Our highest priority wholly-owned product candidate is STRO-004, a single homogeneous ADC directed against tissue factor, or TF, which we are developing for the treatment of solid tumors. We believe STRO-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 submitted an IND and received IND clearance for STRO-004 in October 2025, and initiated a Phase 1 trial in November 2025.

Previous wording

Our other preclinical assets include STRO-006, an ADC targeting Integrinβ6, or Iβ6, and multiple dual-payload ADCs, including iADCs. We believe STRO-006 has the potential to be a best-in-class ADC targeting Iβ6 based on preclinical studies that have demonstrated potent antitumor activity and the potential for a differentiated safety profile. IND enabling activities are underway for STRO-006 that could potentially support an IND filing in connection with this program in the second half of 2026.

Current wording

Our preclinical assets include STRO-227 and STRO-006. STRO-006 is an ADC targeting Integrinß6, or ITGß6. We believe STRO-006 has the potential to be a best-in-class ADC targeting ITGß6 based on preclinical studies that have demonstrated potent antitumor activity and the potential for a differentiated safety profile. IND-enabling activities are underway for STRO-006 that could potentially support an IND submission in connection with this program in 2026.

Previous wording

In addition to STRO-004 and STRO-006, our preclinical portfolio also includes our first wholly-owned dual-payload ADC, a dual-payload ADC targeting Protein Tyrosine Kinase 7, or PTK7. This approach incorporates two distinct cytotoxic payloads, one that is designed to inhibit tubulin and another that is designed to inhibit topoisomerase. We have initiated certain chemistry, manufacturing and controls, or CMC, related activities for the PTK7-targeting dual-payload ADC and anticipate filing an IND in connection with this program in 2027.

Current wording

STRO-227 is our first wholly-owned dual-payload ADC, targeting Protein Tyrosine Kinase 7, or PTK7. This approach incorporates two distinct cytotoxic payloads, one that is designed to inhibit tubulin and another that is designed to inhibit topoisomerase. 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.

Previous wording

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. In addition, we may partner or out-license our wholly owned preclinical or clinical development programs depending on resource and capital availability.

Current wording

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”). Clinical trials for the first iADC licensed pursuant to the Astellas Agreement were initiated in the first quarter of 2026. In addition, we may partner or out-license our wholly-owned preclinical or clinical development programs depending on resource and capital availability.

Previous wording

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 Agreement SM dated April 2, 2021, or the Sales Agreement, with Jefferies LLC, or Jefferies, debt financing, sale of our holdings of Vaxcyte common stock, and the royalty monetization agreement with Blackstone.

Current wording

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, or the Sales Agreement, with Jefferies LLC, or Jefferies, debt financing, sale of our holdings of Vaxcyte common stock, and the royalty monetization agreement with Blackstone.

Previous wording

In March 2025, the 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 a 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, and refocused our activities on our preclinical pipeline, including STRO-004 and STRO-006. In addition, we intend to decommission our San Carlos manufacturing facility by the end of 2025 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. In September 2025, we announced a further reduction in our workforce of approximately one third of our remaining employees, or the September 2025 Restructuring Plan, and, together with the March 2025 Restructuring Plan, the Restructuring Plans, which was intended to further reduce operating costs, streamline operations, and extend our cash runway.

Current wording

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, or CMO, 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 production and have initiated and completed this technology transfer as well. Given the success of these technology transfers, we wound down our manufacturing activities in our San Carlos facility and expect to exit the facility completely in 2026 upon expiration of our leases.

Previous wording

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 $120.3 million and a net loss of $144.3 million for the nine months ended September 30, 2025. We had a loss from operations of $173.2 million and a net loss of $155.0 million for the nine months ended September 30, 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 September 30, 2025, we had an accumulated deficit of $931.2 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 if 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.

Current wording

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 million and a net loss of $38.5 million for the three months ended March 31, 2026. We had a loss from operations of $68.5 million and a net loss of $76.0 million for the three months ended March 31, 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 March 31, 2026, we had an accumulated deficit of $1,016.4 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.

Previous wording

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 Astellas, Vaxcyte, Ipsen, and Tasly, and to a lesser extent, from manufacturing, supply and services and materials we provide to the above collaborators.

Current wording

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 Astellas, Vaxcyte, and other collaborators, and to a lesser extent, from manufacturing, supply and services and materials we provide to the above collaborators.

Previous wording

We derive revenue from collaboration arrangements, under which we may grant licenses to our collaboration partners to further develop and commercialize our proprietary product candidates. We may also perform research and development activities under the collaboration agreements. Consideration under these contracts generally includes a nonrefundable upfront payment, development, regulatory and commercial milestones and other contingent payments, and royalties based on net sales of approved products. Additionally, the collaborations may provide options for the customer to acquire from us materials and reagents, clinical product supply, or additional research and development services under separate agreements. We assess which activities in the collaboration agreements are considered distinct performance obligations that should be accounted for separately. We develop assumptions that require judgement to determine whether the license to our intellectual property is distinct from the research and development services or participation in activities under the collaboration agreements.

Current wording

We derive revenue from collaboration arrangements, under which we may grant licenses to our collaboration partners to further develop and commercialize our proprietary product candidates. We may also perform research and development activities under the collaboration agreements. Consideration under these contracts generally includes a nonrefundable upfront payment, development, regulatory and commercial milestones and other contingent payments, and royalties based on net sales of approved products. Additionally, the collaborations may provide options for the customer to acquire from us materials and reagents, clinical product supply or additional research and development services under separate agreements. We assess which activities in the collaboration agreements are considered distinct performance obligations that should be accounted for separately. We develop assumptions that require judgment to determine whether the license to our intellectual property is distinct from the research and development services or participation in activities under the collaboration agreements.

Previous wording

The following table summarizes our research and development expenses incurred during the indicated periods. The internal costs include personnel, facility costs and research and scientific related activities associated with our pipeline. The external program costs reflect external costs attributable to our clinical development candidates prior to the deprioritization of luvelta and preclinical candidates selected for further development. Such expenses include third-party costs for preclinical and clinical studies and research, development and manufacturing services, and other consulting costs.

Current wording

The following table summarizes our research and development expenses incurred during the indicated periods. The internal costs include personnel, facility costs and research and scientific related activities associated with our pipeline. The external program costs reflect external costs attributable to our clinical development candidates and preclinical candidates selected for further development. Such expenses include third-party costs for preclinical and clinical studies and research, development and manufacturing services, and other consulting costs.

Previous wording

We expect a reduction in research and development expenses throughout 2025 as we strategically reprioritize our resources. However, we anticipate such expenses would increase if we advance our product candidates through clinical development, and continue to develop our external manufacturing capabilities.

Current wording

We expect a reduction in research and development expenses throughout 2026 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 continue to develop our external manufacturing capabilities.

Previous wording

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 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, we anticipate such expenses would increase if we advance our product candidates through clinical development and toward potential commercialization.

Current wording

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.

Previous wording

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 the following restructuring costs in "Restructuring and Related Costs" in our interim condensed Statements of Operations for the three and nine months ended September 30, 2025:

Current wording

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.

Previous wording

Non-cash interest expense related to the sale of future Vaxcyte royalties represents the imputed interest expense on our deferred royalty obligation related to the sale of future Vaxcyte royalties pursuant to the Purchase Agreement, using the effective interest method. As further described in the interim condensed financial statements Note 8. Deferred Royalty Obligation related to the Sale of Future Royalties, in June 2023, we entered into the Purchase Agreement with Blackstone, pursuant to which we sold to Blackstone our 4% royalty, or revenue interest, in the potential future net sales of Vaxcyte’s PCV products, such as VAX-24 and VAX-31.

Current wording

Non-cash interest expense related to the sale of future Vaxcyte royalties represents the imputed interest expense on our deferred royalty obligation related to the sale of future Vaxcyte royalties pursuant to the Purchase Agreement, using the effective interest method. As further described in the interim condensed financial statements in Note 8. Deferred Royalty Obligation related to the Sale of Future Royalties, in June 2023, we entered into the Purchase Agreement with Blackstone, pursuant to which we sold to Blackstone our 4% royalty, or revenue interest, in the potential future net sales of Vaxcyte’s PCV products, such as VAX-24 and VAX-31.

Previous wording

Non-cash interest expense will be recognized over the estimated life of the royalty term arrangement using the effective interest method based on the imputed interest rate derived from the estimated amounts and timing of potential future royalty payments to be earned and received by Blackstone from Vaxcyte under the 2015 License Agreement.

Current wording

Non-cash interest expense will be recognized over the estimated life of the royalty term arrangement 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.

Previous wording

Interest expense includes the financing component under the Astellas Agreement and recorded interest expense associated with the upfront payment.

Current wording

Interest expense primarily includes a financing component under the Astellas Agreement and recorded interest expense associated with the upfront payment.

Previous wording

Total revenue increased by $1.2 million during the three months ended September 30, 2025, as compared to the three months ended September 30, 2024. This was primarily due to a $1.9 million increase from Astellas, of which $0.9 million related to ongoing performance on partially unsatisfied performance obligations under the Astellas Agreement, and a $1.6 million increase in research and development services and materials supply, partially offset by a $0.6 million decrease from the financing component under the Astellas Agreement. Additionally, there was a $0.5 million decrease in Vaxcyte revenue from research and development services.

Current wording

Total revenue decreased by $2.9 million, or 17%, during the three months ended March 31, 2026, as compared to the three months ended March 31, 2025. This was primarily due to a $2.4 million decrease from Astellas, of which $1.0 million related to ongoing performance on partially unsatisfied performance obligations under the Astellas Agreement, a $1.1 million decrease in research and development services and materials supply, and a $0.3 million decrease from the financing component under the Astellas Agreement. Additionally, Other revenue decreased by $0.3 million, primarily due to Ipsen’s decision in the second quarter of 2025 not to advance their partnership with us, and Vaxcyte revenue from research and development services decreased by $0.2 million.

Previous wording

Research and development expense decreased by $22.3 million, or 36%, during the three months ended September 30, 2025, as compared to the three months ended September 30, 2024. The overall decrease was due primarily to decreases of $7.2 million in preclinical research and clinical development expenses, $6.5 million in personnel-related expenses, $4.8 million in outside services, $2.8 million in laboratory supplies, and $1.1 million in allocated facilities and IT-related expenses. 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.

Current wording

Research and development expense decreased by $15.0 million, or 29%, during the three months ended March 31, 2026, as compared to the three months ended March 31, 2025. The overall decrease was due primarily to decreases of $8.0 million in personnel-related expenses, $4.7 million in preclinical research and clinical development expenses, $3.5 million in laboratory supplies, $3.3 million in allocated facilities and IT-related expenses, and $2.1 million in outside services, partially offset by an increase of $6.9 million in technology 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. 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.

Previous wording

General and administrative expense decreased by $5.6 million, or 39%, during the three months ended September 30, 2025, as compared to the three months ended September 30, 2024. The overall decrease was due primarily to decreases of $4.0 million in personnel-related expenses, $1.8 million in outside services, $0.1 million in travel-related expenses, and $0.1 million in equipment and office-related expenses, partially offset by a $0.5 million increase in allocated facilities and IT-related expenses. Some general and administrative 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.

Current wording

General and administrative expense decreased by $5.7 million, or 43%, during the three months ended March 31, 2026, as compared to the three months ended March 31, 2025. The overall decrease was due primarily to decreases of $3.4 million in personnel-related expenses, $2.0 million in outside services, $0.2 million in allocated facilities and IT-related expenses, and $0.1 million in travel-related expenses. Some general and administrative 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.

Previous wording

The following table presents the components of restructuring and related costs from the March 2025 Restructuring Plan, as further described and disclosed in Note 10 to our condensed financial statements:

Current wording

The following table presents the components of restructuring and related costs from the Restructuring Plans, as further described and disclosed in Note 10 to our condensed financial statements:

Previous wording

We will continue to recognize expenses in future periods for the deprioritization of the luvelta program and related costs, of which we expect to recognize a significant portion in 2025. The ultimate amount of expense will be affected by the timing to complete our cost commitments to our third-party CROs and CMOs and the full wind-down of the clinical trials. We will revise our estimates for the costs to deprioritize these studies for the luvelta program and the amount of severance and benefits paid to employees as new information becomes available to us in future periods.

Current wording

We do not expect significant restructuring expenses in future periods for the deprioritization of the luvelta program and related costs. The ultimate amount of expense will be affected by the timing to complete our cost commitments to our third-party CROs and CMOs and the full wind-down of the clinical trials. We will revise our estimates for the costs to deprioritize these studies for the luvelta program as new information becomes available to us in future periods.

Previous wording

Interest income decreased by $2.9 million during the three months ended September 30, 2025, as compared to the three months ended September 30, 2024, due primarily to lower average investment balances and lower average rates of return in 2025.

Current wording

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

Previous wording

Non-cash interest expense increased by $1.8 million during the three months ended September 30, 2025, as compared to the three months ended September 30, 2024. 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.

Current wording

Non-cash interest expense increased by $0.1 million during the three months ended March 31, 2026, as compared to the three months ended March 31, 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.

Previous wording

Interest and other income (expense), net, decreased by $22.9 million during the three months ended September 30, 2025, as compared to the three months ended September 30, 2024, primarily due to a $23.7 million gain on the sale of Vaxcyte common stock recognized during the three months ended September 30, 2024, partially offset by a $0.6 million decrease from the financing component related to the Astellas Agreement and a $0.1 million decrease from foreign exchange fluctuations.

Current wording

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

Previous wording

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 September 30, 2025, we had cash, cash equivalents and marketable securities of $167.6 million, and an accumulated deficit of $931.2 million.

Current wording

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 March 31, 2026, we had cash, cash equivalents and marketable securities of $202.6 million, and an accumulated deficit of $1,016.4 million.

Previous wording

In the first quarter of 2025, we earned a $7.5 million contingent payment from Astellas for their initiation of an IND-enabling toxicology study for the first program under our collaboration with Astellas.

Current wording

In the first quarter of 2025, we earned a $7.5 million contingent payment from Astellas for their initiation of an IND-enabling toxicology study for the first program under our collaboration with Astellas. In the fourth quarter of 2025, we earned a $7.5 million contingent payment from Astellas for their initiation of an IND-enabling toxicology study for the second program under our collaboration with Astellas. In the first quarter of 2026, we earned a $10.0 million contingent payment from Astellas for their dosing of the first subject in a Phase 1 clinical trial in the territory for the first program under our collaboration with Astellas.

Previous wording

In September 2020, we entered into a sublease agreement, (the "Sublease with Five Prime Therapeutics, Inc."), or (the "Sublessor"), for approximately 115,466 square feet, in a building located in South San Francisco, California, or (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 agreement. 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 September 30, 2025 and December 31, 2024.

Current wording

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 March 31, 2026 and December 31, 2025.

Previous wording

Cash used in operating activities for the nine months ended September 30, 2025 was $150.8 million. Our net loss of $144.3 million included non-cash amounts of $28.7 million for non-cash interest expense on our deferred royalty obligation, $12.4 million for stock-based compensation, $5.7 million for depreciation and amortization, $4.3 million for non-cash lease expense, and $2.9 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 $55.1 million, due to a decrease of $69.6 million in deferred revenue resulting from Ipsen's strategic decision not to advance the STRO-003 program under its partnership with us and revenue recognized under the Astellas Agreement, a decrease of $5.5 million in operating lease liabilities, and a decrease of $3.0 million in accounts payable due to timing of payments, partially offset by a decrease of $14.4 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, a decrease of $4.7 million in accounts receivable due primarily to decreases in billing as a result of Ipsen's strategic decision not to advance the STRO-003 program and the completion of technology transfer, and an increase of $3.6 million in accrued expenses and other liabilities due primarily to increases in CMO restructuring costs as a result of the deprioritization of luvelta.

Current wording

Cash used in operating activities for the three months ended March 31, 2026 was $42.3 million. Our net loss of $38.5 million included non-cash amounts of $9.5 million for non-cash interest expense on our deferred royalty obligation, $1.6 million for stock-based compensation, $1.3 million for depreciation and amortization, $1.2 million for non-cash lease expense, and $0.4 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 million, due to a decrease of $9.3 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 million in deferred revenue resulting from revenue recognized under the Astellas Agreement, and an increase of $1.0 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.

Previous wording

Cash used in operating activities for the nine months ended September 30, 2024 was $119.8 million. Our net loss of $155.0 million included non-cash amounts of $32.1 million for the realized gain on the sale of Vaxcyte common stock, $22.4 million for non-cash interest expense on our deferred royalty obligation, $18.8 million for stock-based compensation, $8.2 million for the accretion of discount on marketable securities, $5.4 million for depreciation and amortization, and $3.8 million for non-cash lease expense. Cash used in operating activities also reflected a net change in operating assets and liabilities of $24.6 million, due to a decrease of $29.4 million in accounts receivable primarily from receiving $25.0 million from Vaxcyte as the second of two installment payments for the Option exercise price under the Vaxcyte Agreement, and an increase of $16.1 million in deferred revenue primarily due to the upfront payment from Ipsen, partially offset by revenue recognized under the Astellas Agreement, which were partially offset by a decrease of $10.0 million in accounts payable, accrued expenses and other liabilities due to timing of payments, a decrease of $4.7 million in our operating lease liability, an increase of $4.6 million in prepaid expenses and other assets, and a decrease of $1.5 million in accrued compensation expense primarily due to bonuses paid in 2024 in connection with certain company 2023 goal achievements.

Current wording

Cash used in operating activities for the three months ended March 31, 2025 was $67.9 million. Our net loss of $76.0 million included non-cash amounts of $9.3 million for non-cash interest expense on our deferred royalty obligation, $5.5 million for stock-based compensation, $1.9 million for depreciation and amortization, $1.4 million for non-cash lease expense, and $1.1 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 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 million in deferred revenue primarily due to revenue recognized under the Astellas Agreement, a decrease of $1.7 million in our operating lease liability, and a decrease of $1.3 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 and benefits obligations under the Restructuring Plan. The decrease in operating assets and liabilities were partially offset by an increase of $3.7 million in accounts payable, accrued expenses and other liabilities due to timing of payments.

Previous wording

Cash provided by investing activities of $131.0 million for the nine months ended September 30, 2024 was primarily related to maturities and sales of marketable securities of $394.5 million, and net proceeds from the sale of Vaxcyte common stock of $74.0 million, partially offset by purchases of marketable securities of $335.5 million, and purchases of property and equipment of $2.0 million, principally for laboratory equipment.

Current wording

Cash used in investing activities of $45.3 million for the three months ended March 31, 2026 was primarily related to purchases of marketable securities of $124.7 million, partially offset by maturities of marketable securities of $76.2 million, and sales of marketable securities of $3.2 million.

Previous wording

Cash provided by investing activities of $26.3 million for the nine months ended September 30, 2025 was primarily related to purchases of marketable securities of $260.9 million, and purchases of property and equipment of $1.5 million, principally for laboratory equipment, partially offset by maturities and sales of marketable securities of $251.3 million, and sales of marketable securities of $37.5 million.

Current wording

Cash used in investing activities of $16.3 million for the three months ended March 31, 2025 was primarily related to purchases of marketable securities of $142.4 million, and purchases of property and equipment of $1.2 million, principally for laboratory equipment, partially offset by maturities and sales of marketable securities of $127.3 million.

Previous wording

Cash provided by financing activities of $0.1 million for the nine months ended September 30, 2025 was primarily related to $0.4 million of net proceeds received from participants in our employee equity plans, partially offset by a $0.3 million tax payment related to the net shares settlement of vested restricted stock units.

Current wording

Cash provided by financing activities of $0.1 million for the three months ended March 31, 2025 was primarily related to $0.3 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.

Previous wording

See Note 2 and Note 10 to our interim condensed financial statements for our accounting policies and estimates related to the restructuring and related costs. Other than these accounting policies and estimates, there have been no material changes to our critical accounting policies and estimates discussed in our Annual Report on Form 10-K for the year ended December 31, 2024.

Current wording

There have been no material changes to our critical accounting policies and estimates discussed in our Annual Report on Form 10-K for the year ended December 31, 2025.