Biopharmaceutical company GSK plc (LSE: GSK) (NYSE: GSK) on Monday announced positive results from its global phase I BEHOLD-1 trial evaluating mocertatug rezetecan (Mo-Rez), a B7-H4-targeted antibody-drug conjugate, in gynaecological cancers.

At the highest doses tested, Mo-Rez monotherapy delivered confirmed objective response rates of 62% in platinum-resistant ovarian cancer and 67% in recurrent or advanced endometrial cancer. The data will be presented at the Society of Gynecologic Oncology Annual Meeting in Puerto Rico.

The treatment demonstrated a manageable safety profile, with low discontinuation rates due to treatment-related adverse events and limited incidence of interstitial lung disease. Common adverse events included nausea, while higher-grade events were largely haematologic. Median duration of response has not yet been reached.

GSK highlighted the limited treatment options currently available for these patient groups, noting that the observed efficacy across varying levels of B7-H4 expression supports broader potential for the therapy.

Based on the findings, GSK plans to initiate five pivotal phase III trials in 2026, including studies in ovarian and endometrial cancers across multiple treatment settings. The recommended dose for initial late-stage trials has been set at 5.8 mg/kg.

The BEHOLD programme forms part of GSK's wider oncology strategy, focused on advancing antibody-drug conjugates and expanding its footprint in solid tumours.