GSK reports phase Ib data for Mo-Rez in platinum-resistant ovarian cancer

GSK plc announced updated data from the global phase I BEHOLD-1 trial of mocertatug rezetecan (Mo-Rez) on October 23, 2026, in London. The updated findings come from the global phase I BEHOLD-1 trial for mocertatug rezetecan, an investigational B7-H4-targeted antibody-drug conjugate.¹ The data were set for a late-breaking presentation at the European Society for Medical Oncology Congress 2026 in Madrid, Spain. These data will be presented in a late-breaking oral session at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain.¹

At the selected phase III dose of 5.8 mg/kg, Mo-Rez achieved a confirmed objective response rate of 62% (n=28/45; 95% confidence interval: 46.5-76.2%), with a median duration of response of 12.2 months (95% CI: 7.0-12.7).¹ Median progression-free survival was 11.1 months (95% CI: 8.3-13.9).¹

On safety, results remain consistent with previously published data, with Grade ≥3 treatment-related adverse events observed in 71% (n=32/45) of patients, predominantly haematologic.¹ At the selected phase III dose, treatment-related adverse events led to discontinuation in 2% (n=1/45) of patients, and interstitial lung disease or pneumonitis occurred in 2% (n=1/45) of patients.¹ A total of 136 PROC patients were enrolled in BEHOLD-1, with the most common adverse events at the selected dose being gastrointestinal and haematological; treatment-related adverse events led to dose interruptions in 51% of patients and dose reductions in 47%.¹

GSK said it has moved into late-stage testing. Five pivotal phase III trials are underway: BEHOLD-Ovarian01, BEHOLD-Ovarian02, BEHOLD-Ovarian03, BEHOLD-Endometrial01 and BEHOLD-Endometrial02.¹

On rights, GSK acquired exclusive worldwide rights, excluding mainland China, Hong Kong, Macau and Taiwan, from Hansoh Pharma to progress clinical development and commercialisation of Mo-Rez globally.¹