Regeneron Pharmaceuticals (Nasdaq: REGN) reported a 73% objective response rate and 11-month median progression-free survival for ubamatamab, its MUC16×CD3 bispecific antibody, in 11 heavily pretreated patients with advanced low-grade serous ovarian cancer (LGSOC), with plans to advance the drug into a confirmatory Phase III trial.
LGSOC has historically shown objective response rates below 15% with chemotherapy and endocrine therapy. The only US FDA-approved targeted therapy in the setting, Verastem Oncology's Avmapki Fakzynja Co-pack (avutometinib and defactinib), produced a 44% response rate in patients with KRAS-mutated recurrent LGSOC, a biomarker-defined subgroup representing only a portion of the overall population. Ubamatamab's responses were observed without biomarker selection in patients who had received a median of four prior lines of therapy.
In the ongoing Phase I/II trial, 11 patients with recurrent, heavily pretreated LGSOC who received ubamatamab 800 mg monotherapy had a 73% objective response rate (95% CI: 39.0–94.0), with all responses partial. Median duration of response was 9 months (95% CI: 6.9 to not estimable), while median progression-free survival was 11 months (95% CI: 3.0 to not estimable), according to Regeneron's preliminary results.
Ubamatamab simultaneously binds MUC16 on cancer cells and CD3 on T cells, promoting T-cell-mediated killing of MUC16-expressing tumor cells. Regeneron said LGSOC typically shows high MUC16 expression, potentially allowing the approach to reach patients irrespective of KRAS mutation status.