GSK reported positive Phase I results for mocertatug rezetecan (Mo-Rez), its B7-H4 antibody-drug conjugate, in a BEHOLD-1 study spanning platinum-resistant ovarian cancer and recurrent endometrial cancer. The company said it saw responses across solid tumors, including a 62% response rate in platinum-resistant ovarian cancer patients and 67% in advanced or recurrent endometrial cancer cohorts. Mo-Rez combines a B7-H4-directed monoclonal antibody with a topoisomerase inhibitor payload. GSK said the trial safety profile was manageable, though over 60% of ovarian cancer patients and over 50% of endometrial cancer patients experienced severe adverse events; only 4% overall stopped treatment. GSK said the data support moving into multiple global Phase III trials later this year across ovarian and endometrial cancers. The company also noted the results have not yet been published in a peer-reviewed journal.