Sutro Biopharma (NASDAQ: STRO) posts Q2 2026 loss, advances ADC pipeline
Rhea-AI Filing Summary
Sutro Biopharma reported second quarter 2026 results and detailed progress across its antibody-drug conjugate pipeline. Revenue for the quarter ended June 30, 2026 was $9.8 million, primarily from its Astellas collaboration, down from $63.7 million a year earlier. Total R&D and G&A expenses declined to $39.5 million from $48.7 million, but net loss widened to $38.5 million versus $11.5 million, or $2.33 loss per share compared with $1.35.
Cash, cash equivalents and marketable securities were $164.3 million as of June 30, 2026, versus $202.6 million as of March 31, 2026, and are expected to support operations into at least the second quarter of 2028. Total assets were $194.5 million and total liabilities $297.8 million, including a $239.1 million deferred royalty obligation, resulting in stockholders’ deficit of $103.3 million.
Clinically, the company highlighted STRO-004 Phase 1 data showing multiple confirmed and ongoing unconfirmed partial responses across several tumor types, mostly low-grade adverse events, a 6% discontinuation rate due to adverse events, and dose-proportional pharmacokinetics with a roughly seven-day half-life. Sutro plans to initiate a Phase 1 trial for STRO-006 in the third quarter of 2026 and submit an IND for dual-payload ADC STRO-227 in 2026, while its first Astellas immunostimulatory ADC program has entered the clinic, triggering a $10 million milestone payment.
Positive
- $164.3 million in cash, cash equivalents and marketable securities as of June 30, 2026, with management expecting this balance to fund operations into at least the second quarter of 2028.
- Total R&D and G&A expenses decreased to $39.5 million from $48.7 million year over year, indicating tighter operating spending.
- Early Phase 1 data for STRO-004 show multiple partial responses, a low 6% discontinuation rate due to adverse events, and dose-proportional PK, supporting continued clinical development.
- Pipeline momentum with a Phase 1 trial for STRO-006 expected in 3Q 2026 and an IND submission for dual-payload STRO-227 planned in 2026, plus a partnered iADC already in the clinic.
- Receipt of a $10 million milestone payment from Astellas in April 2026 provides non-dilutive funding linked to partnered program progress.
Negative
- Quarterly revenue fell sharply to $9.8 million from $63.7 million a year earlier, reflecting a large year-over-year decline in collaboration and related income.
- Net loss widened significantly to $38.5 million for the quarter, compared with a loss of $11.5 million in the prior-year period.
- Basic and diluted loss per share increased to $2.33 from $1.35, while weighted-average shares outstanding nearly doubled to 16.6 million, indicating higher per-share losses alongside dilution.
- The balance sheet shows a substantial stockholders’ deficit of $103.3 million and a sizeable $239.1 million deferred royalty obligation related to the sale of future royalties.
Filing Explained
New detail on STRO-004’s current Phase 1 state: dose optimization continues between 4 and 5 mg/kg, while the maximum tolerated dose remains undefined. Dose-limiting toxicities occurred only at 5 mg/kg and caused dose reduction, with no study-drug discontinuations.
8-K Event Classification
Key Figures
Key Terms
antibody-drug conjugate medical
dual-payload ADC medical
deferred royalty obligation financial
dose-limiting toxicity medical
therapeutic index medical
Earnings Snapshot
The company states its cash, cash equivalents and marketable securities are expected to support operations into at least the second quarter of 2028.
AI-generated analysis. How Rhea-AI works. Not financial advice.
FAQ
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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM
CURRENT REPORT
Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934
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Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:
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Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).
Emerging growth company
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐
Item 2.02. Results of Operations and Financial Condition.
On August 12, 2026, Sutro Biopharma, Inc. (the “Company”) issued a press release announcing its financial results for the quarter ended June 30, 2026. A copy of the press release is attached as Exhibit 99.1 to this report.
The information furnished with Item 2.02 of this report, including Exhibit 99.1, is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any other filing under the Exchange Act or under the Securities Act of 1933, as amended (the “Securities Act”), except as expressly set forth by specific reference in such a filing.
Item 7.01. Regulation FD Disclosure.
On August 12, 2026, the Company will be disclosing an updated corporate presentation. A copy of the corporate presentation is attached as Exhibit 99.2 to this report. The corporate presentation will also be available on the Company’s website in the Investors section at https://www.sutrobio.com/corporate-presentation/.
The information furnished with Item 7.01 of this report, including Exhibit 99.2, is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any other filing under the Exchange Act or under the Securities Act, except as expressly set forth by specific reference in such a filing.
Item 9.01. Financial Statements and Exhibits
(d) Exhibits.
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Description |
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99.1 |
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Press release issued by Sutro Biopharma, Inc. regarding its financial results for the quarter ended June 30, 2026, dated August 12, 2026. |
99.2 |
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Corporate Presentation. |
104 |
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Cover Page Interactive Data File (embedded within the Inline XBRL document). |
SIGNATURE
Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
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Sutro Biopharma, Inc. |
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Date: August 12, 2026 |
By: |
/s/ Gregory Chow |
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Gregory Chow |
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Chief Financial Officer |
Exhibit 99.1
Sutro Biopharma Reports Second Quarter 2026 Financial Results and Provides Early Update on STRO-004 Phase 1 Study
– Encouraging early clinical activity including confirmed and ongoing unconfirmed partial responses with favorable tolerability, and pharmacokinetics (PK) observed in ongoing STRO-004 Phase 1 study –
– Strong execution of STRO-004 STRIVE-01 Study with rapid enrollment of initial dose escalation cohorts within 7 months; dose optimization ongoing between 4-5 mg/kg –
– STRO-006, next-generation integrin β6 (ITGB6)-targeting ADC, is on track to enter the clinic in the third quarter of 2026 –
– Second dual-payload iADC program from Sutro’s platform under Astellas collaboration expected to enter the clinic in the second half of 2026 –
– Strong balance sheet with $164.3 million in cash, cash equivalents and marketable securities as of June 30, 2026, expected to support operations into at least the second quarter of 2028 –
SOUTH SAN FRANCISCO, Calif., August 12, 2026 — Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), today reported its financial results for the second quarter ended June 30, 2026 and recent business highlights. Sutro also provided data showing a favorable tolerability profile and early signals of clinical activity from its ongoing Phase 1 study of STRO-004, the Company’s potential best-in-class Tissue Factor (TF)-targeting DAR8 exatecan ADC, in heavily pretreated patients with advanced solid tumors.
“During the second quarter, we continued to execute swiftly across our next-generation ADC portfolio, highlighted by encouraging early clinical data from our ongoing Phase 1 study of STRO-004, having rapidly enrolled our initial dose escalation cohorts in just seven months and now optimizing our go-forward dose,” said Jane Chung, Sutro’s Chief Executive Officer. “We have observed early clinical responses alongside favorable safety, tolerability, and a differentiated pharmacokinetic (PK) profile in patients with few remaining treatment options. The favorable tolerability profile and wider therapeutic index of our DAR8 exatecan ADC allows us to dose higher than other TF-targeting ADCs. These findings strengthen our confidence in STRO-004’s potential to deliver meaningful clinical benefit and provide the opportunity to safely combine with other therapies, while further validating our proprietary ADC platform.”
“Additionally, we are excited to enter the clinic with STRO-006 in the near future, our second clinical program in less than a year, reflecting the continued acceleration of our pipeline strategy. We also look forward to advancing STRO-227, our first wholly-owned dual-payload ADC, toward IND submission later this year, joining our partner Astellas’ dual-payload iADC programs in the clinic. Our progress this quarter underscores the continued advancement of our portfolio and our commitment to delivering differentiated therapies for patients while creating long-term value for shareholders.”
Wholly-Owned Pipeline
STRO-004 Early Safety and Signals of Clinical Activity Highlights:
Dose escalation continues with strong execution, with dose levels 1–5 mg/kg (n=49) enrolled faster than expected. The study, called STRIVE-01, is currently optimizing between doses of 4 and 5 mg/kg, and the maximum tolerated dose has not yet been defined. This US-only based
trial, which began in November 2025, includes heavily pretreated patients (median of 3 prior lines of therapy [range 1–7]) across eight tumor types unselected for TF expression. In pancreatic and colorectal cancer patients, 100% of patients received one or more prior irinotecan-containing regimens, which has been associated with reduced activity of topoisomerase 1 inhibitor payloads. Key observations as of the data cutoff date of July 24, 2026 include:
“We are encouraged by the emerging STRO-004 clinical PK profile, which demonstrate the stability of our ADC construct and validate the design principles of our platform,” said Hans-Peter Gerber, Ph.D., Sutro’s Chief Scientific Officer. “Compared with conventional DAR8 exatecan ADCs, STRO-004 delivered 25-50% more ADC exposure with at least 50% less circulating payload concentration, allowing us to dose at the highest end of the dosing range for the class. We observed comparable PK with STRO-006 (Topo1i) and our dual payload ADC STRO-227 (Topo1i x MMAE) in preclinical experiments, which gives us confidence in the potential of our advanced design capabilities to widen the therapeutic index across our ADC pipeline.”
The next STRIVE-01 study update is targeted for the first half of 2027. Initiation of expansion cohorts is planned for the first half of 2027.
STRO-006: Sutro’s next-generation, highly selective integrin β6 (ITGB6)-targeting ADC with a DAR8 exatecan payload, is designed for the treatment of multiple solid tumors. The Company expects to initiate a Phase 1 clinical trial in the third quarter of 2026.
STRO-227: Sutro’s wholly-owned DAR10 dual-payload ADC targeting PTK7, consisting of MMAE (DAR2) and exatecan (DAR8) payloads to enable complementary mechanisms of action within a
single molecule. The program remains on track for IND submission in 2026 and represents a key component of Sutro’s strategy to expand its pipeline of novel-format dual-payload ADCs.
Next-Generation ADC Collaborations
Astellas: Two research and development programs are progressing under Sutro’s collaboration with Astellas focused on dual-payload immunostimulatory ADCs (iADCs).
The first program, which targets TROP2, continues to actively dose patients, resulting in a $10 million milestone payment received by Sutro in April 2026.
The second program continues to progress under the collaboration, and based on current development timelines, Sutro expects Astellas to enter the clinic by the end of 2026.
Investor Conferences
Management will participate in the following upcoming healthcare investor conferences. When available, the webcasts of the presentations will be accessible through the News & Events page of the Investor Relations section of the Company’s website at www.sutrobio.com. Archived replays will be available for at least 30 days after the event.
Wells Fargo 21st Annual Healthcare Conference (Boston, MA • September 8-10)
Cantor Global Healthcare Conference (New York, NY • September 9-11)
H.C. Wainwright 28th Annual Global Investment Conference (New York, NY • September 14-16)
Second Quarter 2026 Financial Highlights
Cash, Cash Equivalents and Marketable Securities
As of June 30, 2026, Sutro had cash, cash equivalents and marketable securities of $164.3 million, as compared to $202.6 million as of March 31, 2026.
Revenue
Revenue was $9.8 million for the quarter ended June 30, 2026, as compared to $63.7 million for the quarter ended June 30, 2025, with the 2026 amount related principally to the Astellas collaboration.
Research & Development (R&D) and General & Administrative (G&A) Expenses
Total R&D and G&A expenses for the quarter ended June 30, 2026 were $39.5 million, as compared to $48.7 million for the quarter ended June 30, 2025.
About Sutro Biopharma
Sutro Biopharma, Inc. is a clinical-stage biotechnology company advancing a next-generation antibody-drug conjugate (ADC) platform designed to deliver single- and dual-payload ADCs that enable meaningful breakthroughs for patients with cancer. By fully optimizing the antibody, linker, and payload, Sutro’s cell-free platform produces ADCs that are engineered to improve drug exposure, reduce side effects, and expand the range of treatable tumor types. With
unique capabilities in dual-payload ADCs, Sutro aims to overcome treatment resistance and redefine what’s possible in cancer therapy. The Company’s pipeline of single- and dual-payload ADCs targets large oncology markets with limited treatment options and significant need for improved therapies.
For more information, follow Sutro on social media @Sutrobio or visit www.sutrobio.com.
Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, anticipated preclinical and clinical development activities; timing of announcements of IND submissions, trial initiation, clinical results, and other regulatory filings; outcome of discussions with regulatory authorities; potential benefits, efficacy and safety profile of the Company’s product candidates and platform; potential business development and partnering transactions; potential market opportunities for the Company’s product candidates; the positing of the Company’s product candidates in the competitive landscape; the timing and receipt of anticipated future milestone and royalty payments; and the Company’s expected cash runway. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. Although the Company believes that the expectations reflected in such forward-looking statements are reasonable, the Company cannot guarantee future events, results, actions, levels of activity, performance or achievements, and the timing and results of biotechnology development and potential regulatory approval is inherently uncertain. Forward-looking statements are subject to risks and uncertainties that may cause the Company’s actual activities or results to differ significantly from those expressed in any forward-looking statement, including risks and uncertainties related to the Company’s ability to advance its product candidates, the receipt and timing of potential regulatory designations, approvals and commercialization of product candidates, the market size for the Company’s product candidates to be smaller than anticipated, clinical trial sites, supply chain and manufacturing facilities, the Company’s ability to obtain, maintain and recognize the benefits of certain designations received by product candidates, the timing and results of preclinical and clinical trials, the Company’s ability to fund development activities and achieve development goals, the Company’s ability to protect intellectual property, the Company’s commercial collaborations with third parties, the impact of health pandemics, tariffs, regional geopolitical conflicts, changes in interest rates, inflation, potential uncertainty with respect to the debt ceiling and government shutdowns, and other risks and uncertainties described under the heading “Risk Factors” in documents the Company files from time to time with the Securities and Exchange Commission. These forward-looking statements speak only as of the date of this press release,
and the Company undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date hereof.
Investor Contact
Emily White
Sutro Biopharma
(650) 823-7681
ewhite@sutrobio.com
Media Contact
Amy Bonanno
Lyra Strategic Advisory
abonanno@lyraadvisory.com
Sutro Biopharma, Inc.
Selected Statements of Operations Financial Data
(Unaudited)
(In thousands, except share and per share amounts)
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Three Months Ended |
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June 30, |
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2026 |
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2025 |
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Revenue |
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$ |
9,839 |
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$ |
63,745 |
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Operating expenses |
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Research and development |
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31,695 |
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38,325 |
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General and administrative |
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7,831 |
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10,343 |
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Restructuring and related costs |
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201 |
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18,422 |
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Total operating expenses |
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39,727 |
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67,090 |
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Loss from operations |
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(29,888 |
) |
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(3,345 |
) |
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Interest income |
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1,723 |
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2,519 |
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Non-cash interest expense related to the |
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(9,862 |
) |
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(9,647 |
) |
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Interest and other income (expense), net |
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(505 |
) |
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(1,044 |
) |
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Loss before provision for income taxes |
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(38,532 |
) |
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(11,517 |
) |
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Provision for / (benefit) from income taxes |
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1 |
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(18 |
) |
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Net loss |
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$ |
(38,533 |
) |
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$ |
(11,499 |
) |
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Net loss per share, basic and diluted |
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$ |
(2.33 |
) |
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$ |
(1.35 |
) |
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Weighted-average shares used in computing |
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16,571,602 |
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8,511,985 |
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Sutro Biopharma, Inc.
Selected Balance Sheets Financial Data
(Unaudited)
(In thousands)
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June 30, |
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December 31, |
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2026 (1) |
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2025 (2) |
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Assets |
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Cash, cash equivalents and marketable securities |
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$ |
164,346 |
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$ |
141,428 |
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Accounts receivable |
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5,797 |
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3,977 |
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Property and equipment, net |
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8,357 |
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10,648 |
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Operating lease right-of-use assets |
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8,467 |
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10,903 |
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Other assets |
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7,495 |
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6,874 |
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Total Assets |
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$ |
194,462 |
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$ |
173,830 |
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Liabilities and Stockholders’ Equity |
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Accounts payable, accrued expenses and other liabilities |
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$ |
41,476 |
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$ |
58,482 |
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Deferred revenue |
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6,456 |
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12,590 |
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Operating lease liability |
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10,783 |
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15,674 |
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Deferred royalty obligation related to the sale of future royalties |
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239,064 |
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219,536 |
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Total liabilities |
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297,779 |
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306,282 |
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Total stockholders’ deficit |
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(103,317 |
) |
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(132,452 |
) |
Total Liabilities and Stockholders’ Deficit |
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$ |
194,462 |
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$ |
173,830 |
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|
|
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(1)The condensed balance sheet as of June 30, 2026 was derived from the unaudited financial statements included in the Company's Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, filed with the Securities and Exchange Commission on August 12, 2026.
(2) The condensed balance sheet as of December 31, 2025 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2025, filed with the Securities and Exchange Commission on March 23, 2026.
August 2026 NASDAQ: STRO Exhibit 99.2 Sutro Biopharma Logo
This presentation and the accompanying oral presentation contain “forward-looking” statements that are based on our management’s beliefs and assumptions and on information currently available to management. Forward-looking statements include all statements other than statements of historical fact contained in this presentation, including information concerning our future financial performance; business plans and objectives; anticipated preclinical and clinical development activities, including enrollment and site activation; timing of announcements of clinical results, trial initiation, and regulatory filings; outcome of regulatory decisions; and our expectations about our cash runway; potential benefits of our product candidates and platform; potential expansion into other indications and combinations, including the timing and development activities related to such expansion; potential growth opportunities, financing plans, potential future milestone and royalty payments, competitive position, industry environment and potential market opportunities for our product candidates. Forward-looking statements are subject to known and unknown risks, uncertainties, assumptions and other factors, including risks and uncertainties related to our cash forecasts, our and our collaborators’ ability to advance our product candidates, the receipt, feedback and timing of potential regulatory submissions, designations, approvals and commercialization of product candidates and the design, timing and results of preclinical and clinical trials and our ability to fund development activities and achieve development goals. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. These factors, together with those that may be described in greater detail under the heading “Risk Factors” contained in our most recent Annual Report on Form 10-K, Quarterly Report on Form 10-Q and other reports the company files from time to time with the Securities and Exchange Commission, may cause our actual results, performance or achievements to differ materially and adversely from those anticipated or implied by our forward-looking statements. You should not rely upon forward-looking statements as predictions of future events. Although our management believes that the expectations reflected in our forward-looking statements are reasonable, we cannot guarantee that the future results, levels of activity, performance or events and circumstances described in the forward-looking statements will be achieved or occur. Moreover, neither we nor our management assume responsibility for the accuracy and completeness of the forward-looking statements. We undertake no obligation to publicly update any forward-looking statements for any reason after the date of this presentation to conform these statements to actual results or to changes in our expectations, except as required by law. This presentation also contains estimates and other statistical data made by independent parties and by us relating to market size and growth and other data about our industry. This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions, and estimates of our future performance and the future performance of the markets in which we operate are necessarily subject to a high degree of uncertainty and risk. Forward-Looking Statements NON-Confidential
Delivering the Next-Generation of ADC Therapeutics Proprietary Platform Creates Best-in-Class ADCs At the forefront of next-gen ADCs, with improved antibody, linker, and payload for superior safety and efficacy Single-payload ADCs for complex targets where competition is limited Dual-payload ADCs, with partnered and wholly-owned programs, to overcome ADC resistance and delay progression Well-Capitalized Runway into at least the second quarter of 2028 NON-Confidential ITGB6 – Integrin-beta 6; IND – Investigational new drug; TF – Tissue factor; PTK7 – Protein Tyrosine Kinase 7 2H 2025 2026 2026 STRO-004: TF-Targeting ADC STRO-006: ITGB6-Targeting ADC STRO-227: PTK7-Targeting dpADC Three INDs in Two Years Multiple candidates advancing in parallel for large market opportunities
Differentiated Pipeline of Single- and Dual-Payload ADCs NON-Confidential SINGLE-PAYLOAD ADCs: dpADC – Dual-payload ADC; NHP – Non‑human primate; IND – Investigational new drug; ITGB6 – Integrin-beta 6; PTK7 – Protein Tyrosine Kinase 7; TF – Tissue factor Overcome Resistance and Delay Progression DUAL-PAYLOAD ADCs: STRO-227: PTK7-Targeting dpADC Supercharged ADCs with best-in-class potential, combining different payloads to achieve improved clinical benefit, tolerability, and duration of response 2026 IND submission expected Well-tolerated at 25 mg/kg in NHPs Focused on Complex Targets Expressed Across Many Tumor Types STRO-006: ITGB6-Targeting ADC Best-in-class potential, designed for improved clinical benefit, stability, potency, and tumor selectivity Well-tolerated at 30 mg/kg in NHPs Initiation of Ph 1 trial expected 3Q 2026 STRO-004: TF-Targeting ADC Ph 1 trial ongoing; Next update expected 1H 2027 Best-in-class potential, designed for improved clinical benefit, stability, potency, and tumor selectivity Currently dose optimizing between 4-5 mg/kg
Next-Generation ADCs Enabled by Sutro’s Proprietary Platform
Sutro’s Proprietary Cell-free Platform Designed to Optimize Every Component of the ADC Expanding the therapeutic window to minimize toxicity and maximize efficacy Ab – Antibody; DAR – Drug to antibody ratio; ILD – Interstitial lung disease; PK – Pharmacokinetic; TI – Therapeutic index NON-Confidential 4 1 3 4 1 3 2 2 DESIGN FEATURES ADVANTAGES ANTIBODY High-throughput capabilities identifies antibodies with optimized binding, internalization, and developability Fc-silent design Design antibodies for better tumor affinity, avoiding interference with target biology on healthy tissues Reduces Fcγ-mediated toxicities, including ILD NON-NATURAL AMINO ACIDS & CLICK CHEMISTRY Site-selective nnAA incorporation and precise, controlled payload placement via ultra stable bond Homogeneous, stable ADCs with consistent PK, low clearance and minimal free, circulatory payload Reduced platform toxicity ULTRA-STABLE LINKER Stabilized, proprietary β-glu linker designed for tumor-selective cleavage Improves systemic stability and ADC exposure with minimal payload release outside the tumor Low platform toxicity improves the TI PAYLOAD High-DAR and multiple payload combinations with novel payload classes Improves anti-tumor activity and TI Overcomes resistance to prior Topo1 ADCs
Our Proprietary Platform Enables Industry-Leading ADC Exposure, a Key Driver of Safety and Efficacy a b c d e f g h i j STRO-ADC DAR8 Enhertu DAR8 STRO-ADC DAR8 STRO-ADC DAR8 NON-Confidential a. Dato-DXd (DAR4); b. AMT-562-T800 (DAR4); c. ETx-22 (DAR8); d. AMT-562-T1000 (DAR4); e. I-DXd (DAR4); f. PL2201 (DAR6); g. DS-600 (DAR8); h. SKB264 (DAR8); i. DB-1310 (DAR8); j. MTX-13 (DAR8) Ab – Antibody; DAR – Drug to antibody ratio; MMAE – Monomethyl auristatin E; NHP – Non‑human primate; ORR – Overall response rate; PK – Pharmacokinetic Exatecan/Topo1i ADCs Sutro ADC Therapeutics Better PK Less ADC Clearance Less Systemic Toxicity Choosing the right combination of sites can result in optimized pharmacokinetics Site combo A Site combo B Site combo C Site combo D Total Ab (ng/mL) Time post-dose (hr) 100,000 10,000 1,000 100 Conjugated PL Exposure [h ug/mL] PL Dose @ HNSTD [mg/kg] DAR16 ADCs Comparing ADC Exposure in NHPs at Highest Non-Severely Toxic Dose
STRO-004 Potential Best-in-Class Exatecan ADC Targeting Tissue Factor
STRO-004: Potent TF-Targeting DAR8 Exatecan ADC Engineered for Robust Exposure and Efficacy 50x preclinical exposure vs approved TF ADC LINKER β-glu linker with site-specific conjugation for stability and tumor-selective cleavage 3 2 Payload DAR8; safely boosts potency Drives efficacy in low-copy targets Antibody Tumor targeting, does not interfere with TF biology Fc-silent to reduce ILD risk 1 Upcoming milestones Phase 1 trial in a range of solid tumors ongoing; next data update planned for 1H 2027 2 3 1 NON-Confidential DAR – Drug to antibody ratio; ILD – Interstitial lung disease; IND – Investigational new drug; TF – Tissue factor
TF Expression* 35-75% 45-85% 75-80% 45-90% 25-75% Current Std of Care in R/R % ORR mOS (months) 18%1 11-121 8%2 ~62 6-32%3-5 5-83-5 6-40%6-8 11-166-8 13-44%9-11 10-129-11 Significant Unmet Need Across Large Oncology Patient Populations NON-CONFIDENTIAL *TF expression assumptions are based on a weighted average of TF expression as reported in publicly available literature - including but not limited to Johann S. de Bono, et al [2022], Systematic study of tissue factor expression in solid tumors - and triangulated with internal Sutro data on file. Ranges reflect variability across histological subtypes and scoring methodologies. CRC – Colorectal cancer; HNSCC – Head and neck squamous cell carcinoma; ORR – Overall response rate; OS – Overall survival; TF – Tissue factor. *Includes ~60K oral cavity and pharynx plus ~15K larynx. Sources: 1. Vergote et al. 2024; 2. Wang-Gillam 2019; 3. Vermorken 2010; 4. Ferris et al. 2017; 5. Soulieres et al. 2022; 6. Prager et al., 2023; 7. Peeters et al., 2015; 8. Sobrero et al., 2020; 9. Paz-Ares et al. 2024; 10. Ahn et al. 2024; 11. Sands et al. 2025. Incidence (U.S.) and Relapsed/Refractory ORR and OS Benchmarks Across Select Relevant Tumor Types Incidence (U.S.) and relapsed/refractory ORR and OS benchmarks across select relevant tumor types
Dose Level 1 mg/kg Dose Escalation Dose Level 5 mg/kg Dose Level 2 mg/kg Dose Level 3 mg/kg Dose Level 4 mg/kg Detection of activity Characterization of safety profile Early transition to registrational development path Recommended Dose 1 Recommended Dose 2 Move Forward with Recommended Dose(s) HNSCC – Head and neck squamous cell carcinoma; NSCLC – Non-small cell lung cancer; PDAC - Pancreatic ductal adenocarcinoma; GC/EC – gastric cancer/esophageal cancer; TF – Tissue factor; MTD – Maximum tolerated dose NON-Confidential STRO-004 Detailed Monotherapy Development Strategy: Phase 1 STRIVE Trial Ongoing Dose optimization continues between 4-5 mg/kg: MTD not yet defined Next data update planned for 1H 2027 Tumor type eligibility based on prevalence of TF expression: Colorectal Cervical NSCLC HNSCC Bladder PDAC Endometrial GC/EC Currently optimizing between 4-5 mg/kg Initiation of expansion cohorts expected 1H 2027
Data cutoff date: July 24, 2026 PK – Pharmacokinetics; PR – Partial response; PDAC – Pancreatic ductal adenocarcinoma; HNSCC – Head and neck squamous cell carcinoma; NSCLC – Non-small cell lung cancer; CRC – Colorectal cancer; TF – Tissue Factor; AE – Adverse event; MTD –Maximum tolerated dose NON-Confidential STRO-004 Phase 1: Encouraging Early Clinical Activity with Favorable Tolerability & PK Clinical Activity Multiple Responses Confirmed and ongoing unconfirmed responses in PDAC, HNSCC and NSCLC U.S. only, heavily pretreated patient population, across 8 tumor types unselected for TF expression Median 3 prior LOT (range 1–7) 100% of PDAC and CRC patients previously received irinotecan Tolerability & PK Mostly low-grade AEs (Gr 1-2); limited hematologic and on-target TF-related events Low discontinuation rate due to AEs (6%); no discontinuation due to DLTs Dose-proportional exposure; ~7-day half-life, 98% DAR8 and low free circulating payload Planned Next Steps 1H 2027 Next study update Initiation of expansion cohorts Confirmed + ongoing unconfirmed PRs at 3–4 mg/kg Favorable Across Doses 1–5 mg/kg, n=49 Dose Optimization Ongoing between 4–5 mg/kg; MTD not yet defined
NON-Confidential STRO-004 Dose-proportional PK: Cell-free Technology Enables Wider TI with Less Platform Toxicity Cycle 1 geometric mean concentration by dose level; same dose color/symbol is used for both analytes; ADC uses solid lines and free exatecan uses dashed lines. PK – Pharmacokinetics; TI – Therapeutic Index *Garrison & Rowinsky, Clin Can Res, 2003 (Exatecan); Gao & Morales-Barrera, ASCO presentation, 2026 Long half-life of nearly 7 days, maintains 98% DAR8 configuration Free payload below red zone supports lower neutropenia risk* ADC Free exatecan 1 mg/kg 2 mg/kg 3 mg/kg 4 mg/kg 5 mg/kg Highly Stable ADC: High Drug Exposure and Low Levels of Free Payload (below 10 ng/mL) Across Doses
NON-Confidential STRO-004 Favorable Tolerability Profile: Mostly Low-grade AEs with Limited On-target and Platform Tox All-grade TRAEs ≥10% of Subjects and All Gr 3+ Events; Low Discontinuation Rate Due to AEs of 6% Dose Level (n) 1 mg/kg (2) 2 mg/kg (10) 3 mg/kg (13) 4 mg/kg (16) 5 mg/kg (8) Overall (49) Median Prior LoT (Range 1-7) 3.0 3.0 3.0 2.5 4.0 3.0 All Gr Gr 3+ All Gr Gr 3+ All Gr Gr 3+ All Gr Gr 3+ All Gr Gr 3+ All Gr Gr 3+ Any subject with a TRAE: n (%) 1 (50) 0 (0) 5 (50) 0 (0) 10 (77) 3 (23) 13 (81) 5 (31) 7 (88) 4 (50) 36 (73) 12 (24) Nausea 1 (50) 2 (20) 3 (23) 5 (31) 5 (63) 1 (13) 16 (33) 1 (2) Fatigue 2 (20) 7 (54) 3 (19) 2 (25) 14 (29) Anemia 2 (15) 2 (15) 5 (31) 3 (19) 2 (25) 2 (25) 9 (18) 7 (14) Vomiting 1 (10) 2 (15) 2 (13) 2 (25) 7 (14) Diarrhea 1 (10) 4 (25) 1 (13) 6 (12) Epistaxis 1 (10) 1 (8) 3 (19) 1 (13) 6 (12) Decreased appetite 2 (15) 3 (19) 5 (10) Stomatitis 2 (13) 3 (38) 1 (13) 5 (10) 1 (2) ALT increased 1( 8) 2 (13) 1 (6) 1 (13) 4 (8) 1 (2) AST increased 1 (8) 2 (13) 1 (6) 1 (13) 4 (8) 1 (2) Mucosal inflammation 1 (8) 2 (13) 1 (13) 1 (13) 4 (8) 1 (2) Conjunctivitis 2* (15) 1 (8) 2 (25) 4* (8) 1 (2) Neutrophil count decreased 1 (6) 1 (6) 2 (25) 2 (25) 3 (6) 3 (6) Platelet count decreased 1 (6) 2 (25) 1 (13) 3 (6) 1 (2) Blood bilirubin increased 1 (6) 1 (6) 1 (2) 1 (2) Embolism 1 (6) 1 (6) 1 (2) 1 (2) Febrile neutropenia 1 (13) 1 (13) 1 (2) 1 (2) Hypokalaemia 1 (13) 1 (13) 1 (2) 1 (2) Lymphocyte count decreased 1 (6) 1 (6) 1 (2) 1 (2) White blood cell count decreased 1 (13) 1 (13) 1 (2) 1 (2) All-grade TRAEs >15% were nausea (33%), fatigue (29%), anemia (18%) Other TRAEs of note that occurred in >5% of patients included: Hematologic events: neutrophil count decreased (6%), platelet count decreased (6%) On-target TF-related events: epistaxis (12%), stomatitis (10%), mucosal inflammation (8%), conjunctivitis (8%), dry eye (7%); these events were predominantly grade 1-2 Grade 3+ events: anemia (14%) DLTs occurred only in CRC/EGC subjects (4-7 Prior LoT) and only at 5 mg/kg, driven by target-related toxicity; no discontinuations Gr 2/3 stomatitis +/- neutropenia, Gr 2 conjunctivitis Data cutoff date: July 24, 2026; All grade 3+ events were grade 3, except for one grade 4 neutrophil count decrease in the 5 mg/kg cohort * Count increased by 1 manually to capture single event of Gr 3 keratoconjunctivitis Gr – Grade; TRAE – Treatment related adverse events; LOT – Lines of therapy; ALT – Alanine aminotransferase; AST – Aspartate aminotransferase; AE – Adverse event; TF –Tissue Factor; DLT – Dose limiting toxicity; CRC – colorectal cancer; EGC – esophageal/gastric cancer
STRO-006 Potential Best-in-Class Exatecan ADC Targeting Integrin-Beta 6
LINKER β-glu linker with robust in vivo stability to minimize premature release and enhance PK and tolerability 3 Payload High stable DAR8 Potent anti-tumor activity with bystander effect 2 Antibody High affinity to ITGB6 without effect on TGFβ signaling Fc-silent to reduce ILD risk 1 Upcoming milestones Expect to initiate Phase 1 trial in 3Q 2026 2 3 1 STRO-006: Selective ITGB6-Targeting Exatecan ADC for Leading Tolerability and PK STRO-006 is designed for superior selectivity, safety and stability NON-Confidential DAR – Drug to antibody ratio; ILD – Interstitial lung disease; IND – Investigational new drug; ITGB6 – Integrin-beta 6; PK – Pharmacokinetics; TGFβ – Transforming growth factor-beta
ITGB6 Expression has Unique Promise in NSCLC as well as Other Common Solid Tumors STRO-006 is designed for monotherapy and combination use, expanding its therapeutic reach NON-Confidential ITGβ6 expression assumptions are based on a weighted average of expression as reported in publicly available literature and triangulated with internal Sutro data on file. Criteria for positivity differs across studies, overall positive staining/overexpression % is used CRC – Colorectal cancer; HNSCC – Head and neck squamous cell carcinoma; ITGB6 – Integrin beta 6; NSCLC – Non-small cell lung cancer; TNBC – Triple-negative breast cancer
STRO-006 Has Shown Superior Activity at Relevant Doses to Competitor ADCs in CDX Preclinical Models Expressing ITGB6 NON-CONFIDENTIAL Head and Neck (ITGB6+) Lung (ITGB6+) Bladder (ITGB6+) CDX – Cell-line derived xenograft; DAR – Drug to antibody ratio; ITGB6 – Integrin beta-6; MMAE – Monomethyl Auristatin E (tubulin inhibitor); AMDCPT - 7-aminomethyl-10,11-methylenedioxycamptothecin Presented at AACR 2026
Superior Anti-Tumor Activity and Greater Duration of Response With a Single Dose of STRO-006 in HNSCC and NSCLC PDX Models STRO-006 % Best Response PDX Models NON-Confidential BOR – Best overall response; DAR – Drug to antibody ratio; DCR – Disease control rate; HNSCC – Head and neck squamous cell carcinoma; ITGB6 – Integrin beta 6; NSCLC – Non-small cell lung cancer; sq. – Squamous Cell Carcinoma; ad. – adenocarcinoma; ORR – Overall response rate; PDX – Patient-derived xenograft Presented at AACR 2026 STRO-006 5 mg/kg 19 aITGB6 ADC (DAR4. MMAE) 5 mg/kg STRO-006 5 mg/kg ORR: 32/43 (74%) DCR: 35/43 (81%)
Delivering Dual-Payloads: The Next Revolution in ADCs
Dual-Payload ADCs: Potential to Become Future Standard of Care Overcomes resistance resulting from conventional ADCs Reduces toxicity over ADC combination approaches Unique benefits from simultaneous delivery of payloads within the tumor cells Simplified development path compared to combination treatment regimens Unlocks broader market potential across tumor types Combination treatment approaches have been shown to improve outcomes in oncology versus single agent chemotherapy and remain standard of care in many therapeutic areas Dual-Payload ADCs: Targeted Combination Therapy to Improve Outcomes NON-Confidential
Tailored Ratios Proprietary Cell-Free Platform Positions Sutro at the Forefront of Dual-Payload Innovation NON-Confidential Enables novel drug combinations and tuning of ratios with the broadest payload diversity to overcome tumor resistance and improve tolerability Multiple Modalities Well-tolerated in non-human primates at 25 mg/kg (Q3Wx2) with dual cytotoxin ADC Safety Topo1 x Tubulin Topo1 x DDRi Topo1 x IO DAR 4+4 DAR 4+2 DAR 8+4 DAR 8+2 DAR – Drug to antibody ratio; DDRi – DNA damage response inhibitors; IO – Immuno-oncology
Sutro’s First Wholly-Owned Dual-Payload ADC Targeting PTK7 Broad expression across high-need indications and associated with poor prognosis Anti-tumor clinical activity of an anti-PTK7 ADC has been demonstrated across multiple tumor types First-generation anti-PTK7 ADC was constrained by dose-limiting safety, underscoring need for next-generation ADC with greater specificity and a wider therapeutic index NON-Confidential Breast Cancer Xenograft Model Upcoming milestones IND filing anticipated in 2026 A clinically validated, pan-tumor target enriched on tumor-initiating cells PTK7 – Protein Tyrosine Kinase 7; DAR – Drug to antibody ratio; MMAE – Monomethyl auristatin E; IND – Investigational new drug
Broad Anti-Tumor Activity of STRO-227 Across PDX Models STRO-227 % BOR in PDX Models NSCLC STRO-227 Cancer n ORR DCR NSCLC, n (%) 21 12 (57) 16 (76) NON-Confidential DAR – Drug to antibody ratio; DCR – Disease control rate; NSCLC – Non-small cell lung cancer; sq. – Squamous Cell Carcinoma; ad. – adenocarcinoma; ORR – Overall response rate; PDX – Patient-derived xenograft; TNBC – Triple negative breast cancer Presented at AACR 2026 TNBC PDX STRO-227 5 mg/kg Ovarian PDX Dose-dependent anti-tumor activity in TNBC and Ovarian PDX models Comparison of STRO-227 to single-payload benchmarks in TNBC and Ovarian PDX models
Area Target Linker Payload DAR NHP HNSTD Highest Clinical Phase STRO-227 PTK7 β-Glu Exatecan + MMAE 8 + 2 25 mg/kg (Q3Wx2) Preclinical Enhertu HER-2 GGFG Deruxtecan 8 30 mg/kga (Q3Wx3) Approved Datroway Trop-2 GGFG Deruxtecan 4 10 mg/kgb (Q3Wx5) Approved MK-1022 HER-3 GGFG Deruxtecan 8 30 mg/kgc (Q3Wx5) 3 MK-2400 B7-H3 GGFG Deruxtecan 4 30 mg/kgd (Q2Wx3) 3 MK-5909 CDH6 GGFG Deruxtecan 8 30 mg/kge (Q3Wx3) 2/3 Rina-S FOLR1 Val-Cit Exatecan 8 30 mg/kgf (Q3Wx2) 3 aPMID: 27026201 bPMID: 34413126 cPMID: 31471314 dPMID: 35149548 ePMID: 38205802 fDOI:10.1158/1538-7445.AM2023-CT244 Sutro Dual-Payload ADC: Preclinical Tolerability Meets Single-Payload Benchmarks Even with Added MMAE Payload NON-Confidential
Enhertu-Resistant Ovarian Adenocarcinoma Model Sutro’s dpADC Group Dose Total Dose Vehicle --- --- anti-HER2 DAR8 Topo1i 10 mg/kg 10 mg/kg anti-HER2 DAR4 MTi 10 mg/kg 10 mg/kg Co-Administration 10 mg/kg 20 mg/kg 10 mg/kg anti-HER2 dpADC 10 mg/kg 10 mg/kg NON-Confidential DAR – Drug to antibody ratio; MTi – Microtubule inhibitor; dpADC – dual-payload antibody drug conjugate Presented at AACR 2026 Event-Free Survival DAR8+4 dpADC aHER2 DAR8 Exatecan aHER2 DAR4 MTi Co-Administration Vehicle Days Post Dose Relative Tumor Volume (%) Days Post Dose Sutro’s Dual-Payload ADCs Demonstrated Greater Anti-Tumor Activity than Co-administered Single-Payload ADC Survival (%)
Vehicle control Trastuzumab DAR4 MTi (MMAE) ADC (5 mg/kg) Trastuzumab DAR8 Topo1i ADC (5 mg/kg) Trastuzumab DAR8 Topo1i + DAR4 MTi (MMAE) dpADC (5 mg/kg) CRC Xenograft Tumor Growth Curve Mice with Enhertu-resistant tumors were switched onto STRO-002 treatment and subsequently onto dual-payload ADC after exhibiting STRO-002 resistance Dual-Payload ADCs Have Overcome Resistance and Driven Tumor Regression in Preclinical Models 10 mg/kg Enhertu 10 mg/kg STRO-002 10 mg/kg SP12576 NON-Confidential Dual-Payload ADC Induced Tumor Regression After Sequential ADC Resistance Dual-Payload ADCs Have Improved In Vivo Efficacy in an MTi-Resistant CRC Xenograft Model CRC – Colorectal cancer; DAR – Drug to antibody ratio; MMAE – Monomethyl auristatin E; MTi – Microtubule inhibitor
iADC: Dual-Payload ADC Combining Tumor-Targeted Delivery of a Cytotoxin and Immune Stimulator Strategic partnership with Astellas to deliver new treatment options for cold tumors and patients unresponsive to existing cancer immunotherapies Combining a cytotoxin and immune modulator gives potential to: Act alone by stimulating the immune system and priming new populations of immune cells Synergize with other immune therapies that remove inhibitory signals on the immune system (e.g. checkpoint inhibitors) Address hard-to-treat cancers by activating a robust anti-tumor immune response NON-Confidential Partnership Update First program has entered the clinic; patient dosing underway Second program expected to enter clinic in 2H 2026 iADC -- Immunostimulatory ADC; IND – Investigational new drug
Pipeline of Next-Generation Single- and Dual-Payload ADCs PROGRAM MODALITY/TARGET INDICATION DISCOVERY PRECLINICAL PHASE 1/1B PHASE 2 PHASE 3/ REGISTRATIONAL MILESTONES WHOLLY-OWNED PROGRAMS STRO-004 Tissue Factor ADC Solid Tumors Next Phase 1 update expected 1H 2027 STRO-006 Integrin αvβ6 Solid Tumors Phase 1 initiation expected 3Q 2026 STRO-227 PTK7 Dual-Payload ADC Solid Tumors IND submission expected 2026 STRO-00Y Dual-Payload ADC Solid Tumors PARTNERED PROGRAMS VAX-31 31-Valent Conjugate Vaccine Invasive Pneumococcal Disease VAX-24 24-Valent Conjugate Vaccine Invasive Pneumococcal Disease ASP2998 TROP2-targeted Immunostimulatory ADC (iADC) Cancers Entered the clinic 1Q 2026; dosing underway Undisclosed Program iADC Cancers Expected to enter the clinic in 2H 2026 NON-Confidential On track to deliver three programs into the clinic in two years