GSK Ris-Rez B7-H3 ADC Osteosarcoma Phase 3: Second Tumor Win

GSK’s (GSK) licensor Hansoh Pharmaceutical Group announced on July 28, 2026 that ARTEMIS-011, a Phase 3 trial of risvutatug rezetecan (Ris-Rez, HS-20093, GSK5764227) in relapsed osteosarcoma, met its primary endpoint of progression-free survival. The B7-H3-targeted antibody-drug conjugate (ADC) showed statistically significant and clinically meaningful PFS improvement compared with chemotherapy, with consistent benefit across secondary endpoints including overall survival. The safety profile was consistent with prior findings, and no new safety signals emerged. The full press release is on GSK’s site.

GSK closed at $51.98, down $0.05 on the day. The move was negligible for a company with a market cap exceeding $100 billion.

ARTEMIS-011 enrolled patients in China who had relapsed after at least two prior lines of systemic therapy. Hansoh will use the data for a regulatory submission in China. GSK holds exclusive worldwide rights outside mainland China, Hong Kong, Macau, and Taiwan, and is running EMBOLD Sarcoma-202, a global Phase 1b/2 trial in previously treated sarcomas including osteosarcoma.

What B7-H3 is and why it matters

B7-H3 is a cell-surface protein overexpressed across a wide range of solid tumors but with limited expression on normal tissues, making it an attractive ADC target. Ris-Rez pairs a fully human anti-B7-H3 monoclonal antibody with a topoisomerase inhibitor payload. When the antibody binds B7-H3 on a tumor cell, the ADC is internalized and releases the payload inside the cell, killing it from within.

The ARTEMIS-011 result is the second positive Phase 3 for Ris-Rez after ARTEMIS-008, which hit its primary endpoint in advanced or relapsed small-cell lung cancer (SCLC). That makes Ris-Rez the only B7-H3-targeted ADC to deliver positive Phase 3 outcomes across multiple tumor types.

The B7-H3 target is competitive. Daiichi Sankyo’s ifinatamab deruxtecan (I-DXd), co-developed with Merck, has a PDUFA date of October 10, 2026 for previously treated extensive-stage SCLC. If approved, I-DXd would be the first B7-H3 ADC on the market. GSK’s Ris-Rez would follow, but with two Phase 3 wins and an FDA Breakthrough Therapy Designation in osteosarcoma, it is the clinical leader in breadth of proof. For more on the broader ADC competitive picture, see our ADC stocks analysis.

Why osteosarcoma matters

Osteosarcoma is the most common primary bone cancer, mainly affecting children and young adults, with a global incidence of approximately 3.4 cases per million people per year. After patients progress on two prior lines of treatment, there are no approved therapies. The FDA granted Breakthrough Therapy Designation to Ris-Rez in relapsed or refractory osteosarcoma in January 2025.

The China-only Phase 3 means a US approval is not imminent. GSK’s global program (EMBOLD Sarcoma-202) is still in Phase 1b/2, and a global registrational trial has not yet launched. The ARTEMIS-011 data de-risk the target and the drug, but US investors are buying a 2028 or later timeline, not a near-term catalyst.

What to watch

The next catalyst for Ris-Rez is the full ARTEMIS-011 data presentation, expected at a medical congress. Investors should watch for the PFS hazard ratio and median figures, which the press release did not disclose. The specific risk for GSK is that the China-only data may not transfer cleanly to a global population, and the FDA typically requires registrational data from trials that include US sites. Until EMBOLD Sarcoma-202 reads out or GSK initiates a global Phase 3, the US regulatory path remains speculative.