GSK plc filed a Form 6-K on October 26, 2026, reporting updated phase Ib data from the BEHOLD-1 trial showing a 62% confirmed objective response rate for mocertatug rezetecan in platinum-resistant ovarian cancer, with results presented at ESMO Congress 2026 in Madrid, Spain.

Key Highlights

  • 62% confirmed objective response rate: Mo-Rez achieved a cORR of 62% (n=28/45; 95% CI: 46.5-76.2%) at the selected phase III dose of 5.8 mg/kg in platinum-resistant ovarian cancer.
  • 12.2-month median duration of response: Median DoR was 12.2 months (95% CI: 7.0-12.7) at the selected phase III dose.
  • 11.1-month median progression-free survival: Median PFS was 11.1 months (95% CI: 8.3-13.9) in the PROC cohort.
  • Grade 3 or higher adverse events in 71% of patients: Grade 3 or higher treatment-related adverse events were observed in 71% (n=32/45) of patients and were predominantly haematologic.
  • Treatment discontinuation rate of 2%: TRAEs led to treatment discontinuation in 2% (n=1/45) of patients at the selected phase III dose.
  • Five pivotal phase III studies underway: GSK reported that five phase III trials are currently running across ovarian and endometrial cancer indications under the BEHOLD programme.
  • 136 PROC patients enrolled: At data cut-off, a total of 136 platinum-resistant ovarian cancer patients were enrolled in BEHOLD-1.

BEHOLD-1 Phase Ib Results for Mo-Rez in Platinum-Resistant Ovarian Cancer

According to the filing, GSK plc (LSE/NYSE:GSK) announced updated data from the global phase I BEHOLD-1 trial for mocertatug rezetecan (Mo-Rez), described as an investigational B7-H4-targeted antibody-drug conjugate. The data were presented in a late-breaking oral session at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain, with results reflecting more than 13 months of follow-up. The filing states these results build on initial data in platinum-resistant ovarian cancer announced earlier in 2026.

At the selected phase III dose of 5.8 mg/kg, the filing reports a confirmed objective response rate of 62% (n=28/45; 95% CI: 46.5-76.2%), a median duration of response of 12.2 months (95% CI: 7.0-12.7), and median progression-free survival of 11.1 months (95% CI: 8.3-13.9). The filing also discloses that treatment-related adverse events led to dose interruptions in 51% of PROC patients and dose reductions in 47%. Interstitial lung disease or pneumonitis occurred in 2% (n=1/45) of patients at the selected phase III dose.

The filing describes Mo-Rez as composed of a fully human anti-B7-H4 monoclonal antibody covalently linked to a topoisomerase inhibitor payload, with a drug-to-antibody ratio of 6. The company disclosed that it acquired exclusive worldwide rights, excluding mainland China, Hong Kong, Macau, and Taiwan, from Hansoh Pharma to develop and commercialise Mo-Rez globally. The filing notes that five pivotal phase III trials are currently underway across platinum-resistant and platinum-sensitive ovarian cancer, first-line maintenance ovarian cancer, and endometrial cancer settings. The filing contains forward-looking statements that, according to GSK's cautionary language, are subject to risks and uncertainties that may cause actual results to differ materially from those projected.

What Was Disclosed

GSK filed a Form 6-K disclosing updated phase Ib efficacy and safety data from the BEHOLD-1 trial for Mo-Rez in platinum-resistant ovarian cancer, including response rates, survival data, and adverse event profiles, alongside confirmation that five phase III studies are now underway.