GSK plc (LON:GSK, NYSE: GSK) has announced updated data from the global phase I BEHOLD-1 trial for mocertatug rezetecan (Mo-Rez), an investigational B7-H4-targeted antibody-drug conjugate (ADC). Results showed clinically meaningful and durable responses at >13 months follow-up, building on initial data in platinum-resistant ovarian cancer (PROC) announced earlier this year. 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]
Mo-Rez achieved a confirmed objective response rate (cORR) of 62% (n=28/45; 95% confidence interval [CI]: 46.5-76.2%), with a median duration of response (DoR) of 12.2 months (95% CI: 7.0-12.7) at the selected phase III dose of 5.8 mg/kg. Median progression-free survival (PFS) was 11.1 months (95% CI: 8.3-13.9).1
Hesham Abdullah, Senior Vice President, Global Head Oncology, R&D, GSK, said: “Current treatment options for patients with platinum-resistant ovarian cancer are limited and achieving durable responses remains a challenge. These promising results for Mo-Rez show that treatment responses and durability are maintained over time in many patients, alongside encouraging progression-free survival and a manageable safety profile. We have accelerated the phase III development programme across gynaecological cancers, with five pivotal studies now underway.”
Safety results remain consistent with previously published data.[2] Grade ≥3 treatment-related adverse events (TRAEs) were observed in 71% (n=32/45) of patients and were predominantly haematologic. At the selected phase III dose, TRAEs led to treatment discontinuation in 2% (n=1/45) of patients treated and interstitial lung disease (ILD)/pneumonitis occurred in 2% (n=1/45) of patients.1
Vanda Salutari, Study Investigator for BEHOLD-1, Innovative Therapies Unit for Female Cancers, Department of Women and Child Health, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy said: “Despite advances in ovarian cancer, platinum-resistant disease is one of the hardest to treat, and many patients still experience limited benefit from available treatment options. The duration of response and progression-free survival observed in BEHOLD-1 are particularly encouraging relative to what is typically seen in this setting where prolonged disease control remains difficult to achieve.”
B7-H4 is an immune checkpoint that is widely expressed in gynaecological cancers and is low in normal tissues. The responses to Mo-Rez observed across a range of B7-H4 expression levels support its broad potential in gynaecological cancers and an accelerated large-scale phase III programme is now underway in ovarian and endometrial cancers.
Additional data from the BEHOLD programme being presented at ESMO include an exploratory biomarker analysis from BEHOLD-1 showing responses across a range of B7-H4 expression levels and study designs for the phase III BEHOLD-Ovarian01 and BEHOLD-Endometrial01 studies.[3],[4],[5] The BEHOLD-1 results support the selected 5.8 mg/kg dose being evaluated in the phase III development programme.
[1] Salutari V. Mocertatug rezetecan (Mo-Rez) in patients with platinum-resistant ovarian cancer (PROC): Updated results with longer follow-up from the global BEHOLD-1 study. Presented at the European Society for Medical Oncology (ESMO) Congress 2026. October 2026.
[2] Oaknin A, McKean W, van Dongen M, et al. Mocertatug rezetecan (GSK5733584), a B7-H4 targeted antibody drug conjugate, in platinum-resistant ovarian cancer and endometrial cancer: First results from the global BEHOLD-1 study. Presented at the Society of Gynecologic Oncology (SGO) Annual Meeting on Women’s Cancer 2026. April 2026.
[3] Lheureux S. BEHOLD-1: Exploratory analysis of biomarkers associated with mocertatug rezetecan (Mo-Rez) response in patients with platinum-resistant ovarian cancer (PROC). Presented at the European Society for Medical Oncology (ESMO) Congress 2026. October 2026.
[4] Backes F. BEHOLD-Ovarian01: A Phase 3 randomised trial to evaluate mocertatug rezetecan (Mo-Rez) versus standard of care (SoC) in patients (pts) with platinum-resistant ovarian cancer (PROC). Presented at the European Society for Medical Oncology (ESMO) Congress 2026. October 2026.
[5] Oaknin A. BEHOLD-Endometrial01: A randomised Phase 3 study evaluating the efficacy and safety of mocertatug rezetecan (Mo-Rez) versus chemotherapy in patients with advanced or recurrent endometrial cancer after platinum-based therapy and immunotherapy. Presented at the European Society for Medical Oncology (ESMO) Congress 2026. October 2026.
