GSK reported positive early clinical data from its Phase I BEHOLD-1 trial of mocertatug rezetecan (Mo-Rez), an antibody-drug conjugate targeting B7-H4, in platinum-resistant ovarian cancer and recurrent endometrial cancer. Across the trial dataset, GSK said response rates were 62% in PROC patients and 67% in advanced or recurrent endometrial cancer patients, alongside a safety profile that the company characterized as manageable. GSK also said the rates were notable in the context of a disease setting where platinum resistance remains common. The company indicated it plans to accelerate development into five pivotal Phase III trials later this year across both tumor types. It also noted that severe adverse events were experienced by more than half of PROC patients and more than half of endometrial patients, with only a small fraction discontinuing treatment. Because the results are not yet published in a peer-reviewed journal, the near-term focus will shift to confirmatory efficacy and tolerability in the planned Phase III programs.