Ubamatamab produces high rate of durable responses in early study of advanced low grade serous ovarian cancer

Regeneron has reported the first results for its investigational bispecific antibody ubamatamab in patients with low grade serous ovarian cancer (LGSOC). The data come from an ongoing Phase 1/2 trial in recurrent, platinum resistant high or low grade serous ovarian cancer and were presented in a late breaking plenary oral session at the International Gynecologic Cancer Society 2026 Annual Global Meeting. Ubamatamab links MUC16 on cancer cells to CD3 on T cells, with the aim of triggering T cell activation at the tumour.

Because of these early results, Regeneron has been enrolling a single arm, potentially registrational trial in LGSOC and plans to discuss the data with the US Food and Drug Administration over the coming months. The company also intends to launch a confirmatory, randomised, controlled Phase 3 trial to support the use of ubamatamab in the disease.

LGSOC is biologically distinct from the more common high grade serous ovarian cancer (HGSOC) and makes up as much as 10 per cent of serous ovarian cancers. It typically shows uniformly high MUC16 expression, offers few treatment options and often affects younger women. Its tumours grow more slowly than those of HGSOC, but they frequently come back and respond poorly to conventional chemotherapy. Median overall survival from diagnosis is about seven years in LGSOC, compared with about four years in HGSOC. In recurrent advanced LGSOC, historical trials show objective response rates generally under 15 per cent with chemotherapy and endocrine therapy. The only approved therapy has an objective response rate of 44 per cent, but only in biomarker selected patients, who account for roughly 30 per cent of people with LGSOC.

The data presented covered a subset of 19 LGSOC patients who had received a median of four earlier lines of therapy. They were given intravenous ubamatamab at doses from 3 mg to 800 mg, weekly or every three weeks, either alone or combined with Libtayo® (cemiplimab). The presentation focused on 11 patients who received 800 mg of ubamatamab alone, eight of them weekly and three every three weeks. At the 800 mg doses, the objective response rate was 73 per cent (95% CI 39.0 to 94.0), and every response was a partial response. Median duration of response was 9 months (95% CI 6.9 to not estimable) and median progression free survival was 11 months (95% CI 3.0 to not estimable), both by Kaplan-Meier estimate.

Safety was assessed in all 19 patients. Every patient had a treatment emergent adverse event. Cytokine release syndrome affected 90 per cent (17 patients), all of it grade 1 or 2. Serious treatment emergent events of grade 3 or higher occurred in 21 per cent (four patients), and treatment related adverse events occurred in 74 per cent (14 patients). Grade 3 or higher treatment related events were neutropenia in 21 per cent (four patients), anaemia in 11 per cent (two), raised alanine aminotransferase in 11 per cent (two), raised aspartate aminotransferase in 11 per cent (two), abdominal pain in 5 per cent (one) and ileus in 5 per cent (one). Most adverse events occurred during the step up dosing period. One participant stopped treatment because of a stroke judged unrelated to ubamatamab, and no adverse event led to death.

Israel Lowy, M.D., Ph.D., clinical development unit head for oncology at Regeneron, said the high rate of durable responses seen so far, without any need to select patients by biomarker, is highly encouraging and strengthens the company’s enthusiasm for MUC16 as a new target in this hard to treat disease. He said the early evidence shows the potential of the bispecific approach to offer a differentiated, first in class option to patients in need. He added that Regeneron is pleased with the drug’s safety profile and eager to build on the findings through the ongoing trial and the planned Phase 3.

The potential uses of ubamatamab described here are investigational, and no regulatory authority has evaluated its safety or efficacy.

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Related Topics and Keywords

Cancer, Ovarian Cancer, Ubamatamab