STRO

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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:

• Multiple responses, including confirmed and ongoing unconfirmed partial responses, across three tumor types in RECIST-evaluable patients to date; including pancreatic cancer, head and neck cancer, and non-small cell lung cancer at dose levels 3-4 mg/kg

• Favorable tolerability profile, with mostly low-grade adverse events (AEs) observed. Overall discontinuation rate due to AEs was low at 6%.

o All-grade treatment related adverse events (TRAEs) >15% were nausea (33%), fatigue (29%), and anemia (18%)

o 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%); all grade 3

o DLTs occurred only at the highest dose level tested (5 mg/kg), and appeared to be largely driven by target-related toxicity, resulting in dose redu

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Exhibit 99.1

Sutro Biopharma Reports First Quarter 2026 Financial Results and Business Highlights

– On track to report initial safety, PK and early activity from Phase 1 dose-escalation trial of STRO-004, potential best-in-class Tissue Factor ADC, in mid-2026 –

– Continued advancement of wholly-owned pipeline, including ITGB6 ADC STRO-006 and dual-payload PTK7 program STRO-227, with IND submissions planned in 2026 –

– First dual-payload iADC from Sutro’s platform entered the clinic under Astellas collaboration; patient dosing underway –

– Strong balance sheet with $202.6 million in cash, cash equivalents and marketable securities as of March 31, 2026; including gross proceeds from the recent capital raise, supporting operations into at least the second quarter of 2028 –

SOUTH SAN FRANCISCO, Calif., May 14, 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 first quarter of 2026 and recent business highlights.

“During the first quarter, we continued to execute across our clinical and preclinical portfolio, positioning Sutro for key data readouts later this year,” said Jane Chung, Sutro’s Chief Executive Officer. “Dose escalation is rapidly progressing in our Phase 1 trial of STRO-004, and we remain on track to report initial safety, pharmacokinetic and early activity data in mid-2026, which we believe will provide important insights into its clinical profile and our platform as a whole. This clinical momentum is reinforced by preclinical data we presented at the recent AACR Annual Meeting, which highlighted the robust and consistent antitumor activity of STRO-004, as well as continued progress across our broader ADC pipeline.”

“In parallel, we are advancing our next-generation ADC candidates, STRO-006, targeting ITGB6, and STRO-227, our first wholly-owned dual-payload ADC targeting PTK7, as we work toward IND submissions this year. We are also pleased to see our first partnered dual-payload iADC with Astellas entering the clinic, marking an important validation of our platform’s ability to generate differentiated multi-payload ADCs. With a strengthened balance sheet and continued disciplined execution, we believe we are well positioned to deliver meaningful progress across our programs in 2026.”

Wholly-Owned Pipeline

STRO-004: Sutro continues to advance its ongoing first-in-human Phase 1 dose-escalation trial of STRO-004, a Tissue Factor (TF)-targeting ADC with a DAR8 Topo1 payload, in patients with advanced solid tumors. The Company expects to report initial clinical data in mid-2026, including safety and tolerability, pharmacokinetic exposure, and early activity data. In preclinical studies, STRO-004 demonstrated a favorable safety profile, including a highest non-severely toxic dose (HNSTD) of 50 mg/kg in non-human primates, supporting the clinical starting dose of 1 mg/kg.

STRO-006: Sutro’s next-generation, highly selective integrin β6 (ITGB6)-targeting ADC with a DAR8 Topo1 payload, designed for the treatment of multiple solid tumors. The program continues to advance toward clinical development, with an IND submission anticipated in 2026.

STRO-227: Sutro’s wholly-owned DAR10 dual-payload ADC targeting PTK7, combining MMAE (DAR2) and a Topo1 payload (DAR8) 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, targeting TROP2, has entered the clinic and is actively dosing patients, resulting in a $10 million milestone payment received by Sutro in April 2026.

• The second program continues to progress in an IND-enabling toxicology study.

Medical Conferences

American Association for Cancer Research (AACR), April 17-22, 2026, San Diego, California

• Sutro presented new preclinical data at AACR from across its pipeline of ADC discovery programs, including an oral presentation on STRO-004. Among the highlights, STRO-004 demonstrated robust and consistent antitumor activity across multiple TF-expressing solid tumor PDX models, with improved anti-tumor activity versus benchmark ADCs. Additionally, STRO-006 and STRO-227 showed meaningful, dose-dependent antitumor activity across solid tumor models. More details can be found in the press release here.

• In addition to these presentations, Sutro’s strategic partner, Astellas Pharma, also reviewed preclinical results from its TROP2-targeted iADC program, ASP2998, at AACR. The oral presentation, titled “ASP2998, a TROP2-targeted immunostimulato

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Exhibit 99.1

Sutro Biopharma Reports Full Year 2025 Financial Results and Business Highlights

– Dosed three cohorts in Phase 1 trial of STRO-004, potential best-in-class Tissue Factor (TF) ADC; on track to report initial clinical data in mid-2026 –

– Company announced first wholly owned dual-payload program targeting PTK7, STRO-227, accelerating IND submission to 2026 –

– Astellas-partnered iADC dual-payload program enters the clinic; patient dosing underway –

– Cash, cash equivalents and marketable securities as of December 31, 2025 of $141.4 million, excluding proceeds from the recent capital raise of approximately $110 million which extended cash runway into at least the second quarter of 2028 –

SOUTH SAN FRANCISCO, Calif., March 23, 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 full year 2025 and recent business highlights.

“2026 is poised to be a pivotal year, propelled by disciplined clinical execution and initial data that we believe will showcase the vast potential of our proprietary ADC platform,” said Jane Chung, Sutro’s Chief Executive Officer. “We recently completed dosing the third cohort in the Phase 1 trial of STRO-004, our potential best-in-class Tissue Factor ADC, and look forward to reporting initial data mid-year. In parallel, we are advancing STRO-006, our ITGB6 ADC, and accelerating STRO-227, our wholly owned dual-payload program targeting PTK7, toward IND submission this year. In addition, patient dosing has commenced under our collaboration with Astellas Pharma for our first partnered dual-payload iADC — marking the first dual-payload program from Sutro’s platform to enter the clinic. Supported by our recent financing, continued financial stewardship, and sharpened strategic focus, we believe we are well positioned to execute across all our programs and deliver differentiated ADCs with best-in-class potential that could redefine standards of care in oncology.”

Wholly Owned Pipeline

STRO-004: The Company has completed dosing across three cohorts in the first-in-human Phase 1 trial evaluating STRO-004, a DAR8 Topo1 ADC targeting Tissue Factor (TF), with potential as best-in-class TF ADC. Initial clinical data are expected in mid-2026, including safety and tolerability. Sutro also expects to share pharmacokinetic exposure and potentially early signs of activity. In non-human primate studies, STRO-004 demonstrated a favorable preclinical safety profile, with a highest non-severely toxic dose (HNSTD) of 50 mg/kg — supporting a clinical starting dose of 1mg/kg.

STRO-006: A highly selective, DAR 8 Topo1 ADC targeting integrin β6 (ITGB6), STRO-006 is expected to enter clinical development in 2026 for the treatment of multiple solid tumors.

STRO-227: Sutro’s PTK7-targeting dual-payload ADC program, consisting of MMAE (DAR2) and Topo1 (DAR8), remains on track, with an IND submission targeted for 2026.

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, targeting TROP2, has entered the clinic and is actively dosing patients, triggering a $10 million milestone payment with receipt expected in the second quarter of 2026.

• The second program entered an IND-enabling toxicology study in the fourth quarter of 2025, triggering a $7.5 million milestone payment to Sutro.

Upcoming and Recent Industry/Medical Conferences

American Association for Cancer Research (AACR), April 17-22, 2026, San Diego California

• Sutro’s strategic partner, Astellas Pharma, will present preclinical results from its TROP2-targeted iADC program in an oral presentation on Sunday, April 19, 2026 at 4:35-4:50 PM PT. The presentation, titled “ASP2998, a TROP2-targeted immunostimulatory antibody-drug conjugate (iADC) with dual payloads, demonstrates potent efficacy and a favorable safety profile in nonclinical models,” highlights progress in the development of next-generation iADCs leveraging Sutro’s cell-free protein synthesis platform.

• Additionally, Sutro will present an oral presentation and multiple posters highlighting advances across its ADC pipeline and discovery platforms at AACR. The presentation details are as follows:

o

Presentation: “STRO-004, an exatecan-based next-generation tissue factor (TF)-targeted ADC, demonstrates superior efficacy across TF-expressing solid tumors in a comprehensive single-mouse PDX trial”

•

Presentation Date and Time: Sunday, April 19, 2026; 4:35-4:50 PM PT

o Poster: “Phase 1 open-label study to evaluate safety, pharmacokinetics, and preliminary anti-tumor activity of STRO-004 in adults with refractory/recurrent metastatic solid tumors”

• Session Date and Time: Monday, April 20, 2026; 9:00