London, United Kingdom, U.S., October 23, 2026
GSK plc announced updated clinical data for mocertatug rezetecan (Mo-Rez), an investigational antibody-drug conjugate (ADC), demonstrating durable responses in patients with platinum-resistant ovarian cancer (PROC). The findings from the global Phase 1 BEHOLD-1 study showed a confirmed objective response rate of 62% and a median duration of response of 12.2 months at the selected Phase 3 dose of 5.8 mg/kg. Median progression-free survival reached 11.1 months, highlighting the candidate’s potential in a difficult-to-treat cancer setting where treatment options remain limited. GSK announced the updated results on October 23, 2026, ahead of their presentation in a late-breaking oral session at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain. The results build on earlier clinical findings and support continued investigation of Mo-Rez across gynaecological cancers. The candidate remains investigational and requires further evaluation in larger clinical trials to establish its safety and effectiveness.
Mo-Rez Shows Durable Responses in Platinum-Resistant Ovarian Cancer
The updated BEHOLD-1 analysis evaluated Mo-Rez at the selected Phase 3 dose of 5.8 mg/kg in patients with platinum-resistant ovarian cancer. Among 45 patients included in the reported analysis, 28 achieved a confirmed objective response, corresponding to a response rate of 62%, with a 95% confidence interval of 46.5% to 76.2%. The median duration of response was 12.2 months, indicating that responses persisted for a meaningful period among patients who responded to treatment. Median progression-free survival was 11.1 months, with a 95% confidence interval of 8.3 to 13.9 months. These results were reported after more than 13 months of follow-up and demonstrate continued clinical activity in a population that can be challenging to treat. Platinum-resistant ovarian cancer occurs when disease progresses or returns despite platinum-based chemotherapy, a key component of standard ovarian cancer treatment. The findings are encouraging, although response rates from an early-phase study should not be interpreted as proof of comparative benefit over existing therapies. Further randomized Phase 3 studies will be needed to establish whether Mo-Rez can improve patient outcomes.
Safety Findings Inform Mo-Rez Clinical Development
GSK reported that the safety profile remained consistent with previously presented BEHOLD-1 findings. At the selected Phase 3 dose, Grade 3 or higher treatment-related adverse events occurred in 71% of patients, or 32 of the 45 participants included in the analysis. These events were predominantly haematological, meaning they affected blood cells or blood-forming systems. Treatment-related adverse events led to treatment discontinuation in one patient, representing 2% of the group. Interstitial lung disease or pneumonitis occurred in one patient, also representing 2%. Across the wider platinum-resistant ovarian cancer population enrolled in BEHOLD-1, gastrointestinal and haematological events were among the most common adverse events. Dose interruptions and reductions were also reported during the study, reflecting the importance of managing treatment-related toxicity. The safety results will be important as GSK evaluates Mo-Rez in larger trials, where the benefit-risk profile can be assessed in broader patient populations. The investigational therapy’s response durability and progression-free survival findings need to be considered alongside these safety observations when determining its future clinical role.
Advertisement
GSK Expands Phase 3 Programme Across Gynaecological Cancers
Mo-Rez is a B7-H4-targeted antibody-drug conjugate designed to deliver a topoisomerase inhibitor payload to cancer cells expressing B7-H4, a protein found in several gynaecological cancers and reported to have low expression in normal tissues. The candidate consists of a fully human monoclonal antibody linked to a cytotoxic drug payload, with a drug-to-antibody ratio of six. This approach aims to direct anticancer activity toward tumour cells while supporting targeted delivery of the payload. GSK obtained exclusive worldwide development and commercialization rights to Mo-Rez, excluding mainland China, Hong Kong, Macau and Taiwan, from Hansoh Pharma. The company reported that five pivotal Phase 3 studies are now underway across ovarian and endometrial cancers. These include trials in platinum-resistant and platinum-sensitive ovarian cancer, ovarian cancer maintenance settings, and advanced or recurrent endometrial cancer. The broader programme reflects GSK’s strategy to develop targeted treatments for cancers where resistance and limited therapeutic options continue to create substantial unmet medical needs. Mo-Rez is not an approved medicine, and its clinical value will depend on results from ongoing confirmatory studies and regulatory review.
Source: GSK press release
