GSK Reports Strong Phase I Data for Mo-Rez Cancer Therapy

GSK plc has announced positive results from its global Phase I BEHOLD-1 clinical trial for mocertatug rezetecan (Mo-Rez), a novel antibody-drug conjugate (ADC) designed to target the B7-H4 antigen. The therapy is aimed at patients with gynecologic cancers who currently have limited treatment options and modest response rates. At the highest doses evaluated, Mo-Rez monotherapy demonstrated significant efficacy, achieving confirmed objective response rates of 62% in platinum-resistant ovarian cancer (PROC) and 67% in recurrent or advanced endometrial cancer (EC). The B7-H4 antigen is widely expressed in these specific cancers but remains low in normal tissues, allowing for a more precise therapeutic approach. Safety data from the BEHOLD-1 trial indicated that the treatment was generally well-tolerated. Discontinuation rates due to treatment-related adverse events were 0% for PROC patients and 4% for EC patients. While nausea was the most common side effect, affecting 82% of PROC and 75% of EC patients, rates of severe interstitial lung disease or pneumonitis remained low. Grade 3 treatment-related adverse events occurred in 64% of PROC and 54% of EC patients, primarily involving hematologic issues consistent with this class of therapy. Interim analysis shows that the median duration of response has not yet been reached. Following these results, GSK has established a recommended dose of 5.8 mg/kg for upcoming trials. The company intends to leverage this efficacy and safety profile to launch five pivotal Phase III trials in 2026, including the BEHOLD-Ovarian01 and BEHOLD-Endometrial01 studies.