GSK reported positive Phase I results from BEHOLD-1 for its B7-H4-directed antibody-drug conjugate mocertatug rezetecan (Mo-Rez) in platinum-resistant ovarian cancer and recurrent endometrial cancer. The company said the ADC produced responses in 62% of platinum-resistant ovarian cancer patients and 67% of endometrial patients. GSK said the safety profile was manageable, while acknowledging that over 60% of ovarian cancer patients and over 50% of endometrial cancer patients experienced severe adverse events. The company indicated it plans to accelerate development into five global Phase III trials later in 2026. BEHOLD-1 data were not reported as peer-reviewed in the release. Still, the response rates provided a potentially high bar for the ADC’s positioning in settings where platinum resistance limits standard chemotherapy options.