GSK Reports Strong Results for B7-H4 ADC in Gynecological Cancers

Why It Matters

The high response rates address a critical unmet need in refractory gynecologic cancers and could position Mo‑Rez as a leading ADC, reshaping treatment standards and expanding GSK’s oncology portfolio.

Key Takeaways

• Mo-Rez achieved 62% ORR in platinum-resistant ovarian cancer
• 67% response observed in recurrent/advanced endometrial cancer
• B7-H4 expression broad, enabling treatment beyond biomarker‑positive patients
• GSK will launch five Phase III ADC trials starting 2026

Pulse Analysis

The Phase 1 BEHOLD‑1 trial has placed GSK’s B7‑H4‑directed antibody‑drug conjugate, mocertatug rezetecan (Mo‑Rez), on the radar of oncologists treating gynecologic malignancies. 8 mg/kg dose, the agent produced a confirmed objective response rate of 62 % in platinum‑resistant ovarian cancer and 67 % in recurrent or advanced endometrial cancer—far exceeding the single‑digit to low‑teens response rates typical of chemotherapy or hormonal options in these refractory settings. Such early efficacy signals are especially compelling given the limited therapeutic armamentarium for patients who have exhausted first‑line regimens.

B7‑H4’s restricted expression on tumor cells and minimal presence in normal tissue makes it an attractive immuno‑oncology target, and Mo‑Rez appears to retain activity across a spectrum of expression levels. This breadth could sidestep the biomarker‑driven constraints that have hampered other ADC programs. Safety findings were consistent with the class, with nausea as the most common adverse event and manageable hematologic toxicities; rates of interstitial lung disease remained low. Compared with rival ADCs such as mirvetuximab soravtansine, Mo‑Rez’s response rates suggest a potency advantage while maintaining a tolerable profile.

Building on the Phase I data, GSK has outlined an ambitious five‑trial Phase III program slated for 2026, covering platinum‑resistant and platinum‑sensitive ovarian cancer, second‑line and maintenance settings in endometrial cancer, and first‑line maintenance in ovarian disease. If the registrational studies confirm durability and safety, Mo‑Rez could capture a sizable share of a market projected to exceed $5 billion by 2030, reinforcing GSK’s position in the rapidly expanding ADC space. Moreover, a successful B7‑H4 validation would likely spur additional investment in checkpoint‑directed ADCs across solid tumors.