Regeneron Pharmaceuticals (NASDAQ: REGN) announced results from an early-stage trial of its investigational drug ubamatamab in patients with low-grade serous ovarian cancer (LGSOC), showing a 73% objective response rate among the most heavily dosed patients.

The data, drawn from an ongoing Phase 1/2 trial, were presented at the International Gynecologic Cancer Society 2026 Annual Global Meeting. The results focused on 11 patients treated with 800 mg of ubamatamab as monotherapy, who had previously received a median of four prior lines of therapy.

At the 800 mg dose, the trial showed a 73% objective response rate (95% CI: 39.0 to 94.0), a 9-month median duration of response, and an 11-month median progression-free survival. All responses were partial responses.

Safety data across all 19 LGSOC patients showed treatment-emergent adverse events in 100% of participants. Cytokine release syndrome occurred in 90% of patients, all graded as Grade 1 or 2. Serious adverse events of Grade 3 or higher occurred in 21% of participants. One patient discontinued treatment due to a stroke considered unrelated to the drug; no adverse events resulted in death.

Ubamatamab is a MUC16xCD3 bispecific antibody designed to connect MUC16-expressing cancer cells with T cells to stimulate a local immune response. LGSOC accounts for up to 10% of serous ovarian cancer cases and has historically shown objective response rates below 15% with standard chemotherapy.

Regeneron said it is currently enrolling a single-arm, potentially registrational LGSOC cohort at the 800 mg dose and plans to discuss the data with the U.S. Food and Drug Administration. The company also said it intends to initiate a confirmatory randomized Phase 3 trial. Ubamatamab remains investigational and has not been approved by any regulatory authority.