Agenus reports three-year survival data for ovarian cancer immunotherapy combo

Agenus Inc. has reported that 48 percent of patients in a recurrent ovarian cancer study were alive three years after receiving its experimental immunotherapy combination. The three-year overall survival estimate was unchanged from the two-year mark, suggesting a durable benefit. The results from the Phase 1b trial were presented Saturday at the International Gynecologic Cancer Society annual meeting in Montreal. The study involved patients who had received a median of four prior lines of therapy, and nearly three quarters had cancer that was resistant to standard platinum chemotherapy.

Among the 35 patients evaluable for efficacy, the objective response rate was 23 percent, including one complete response and seven partial responses. The median duration of response was 9.7 months, and 31 percent of patients had a response or stable disease lasting at least 24 weeks. At the last follow-up, 11 of the 44 patients who received at least one dose of treatment were alive and off all therapy. "In recurrent ovarian cancer, conventional checkpoint immunotherapy has rarely produced lasting benefit, particularly after the disease stops responding to platinum chemotherapy," said Rebecca L. Porter, a doctor at Dana-Farber Cancer Institute who presented the data. "What stands out with longer follow-up is the survival plateau in patients who had already received multiple treatments. That pattern suggests that a different approach to activating the immune system may offer some patients lasting benefit, even when treatment options have narrowed."

The patients in the study were heavily pretreated. All had previously received platinum chemotherapy, 77 percent had received bevacizumab and 57 percent had received a PARP inhibitor. In a subgroup of 25 patients with platinum-resistant or refractory disease, the estimated three-year survival was 47 percent. For the 10 patients with platinum-sensitive disease, the estimate was 45 percent.

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"The most compelling finding is that the survival curve extends beyond two years in women who had already received multiple treatments, including those with platinum-resistant or refractory disease," said Steven J. O'Day, chief medical officer of Agenus. "We have seen a similar pattern of durable survival in other difficult-to-treat cancers studied with BOT+BAL. This three-year ovarian update strengthens our conviction that the combination can deliver meaningful, lasting benefit to a subset of patients who have had few effective immunotherapy options." The safety profile remained consistent with what was previously known for the drug combination, and no new safety signals or treatment-related deaths were reported. The therapy pairs botensilimab, an anti-CTLA-4 antibody, with balstilimab, an anti-PD-1 antibody. Both drugs are investigational and have not been approved by the U.S. Food and Drug Administration.

The three-year ovarian results add to data from other difficult-to-treat cancers. In a broader analysis of over 400 patients across tumor types, the estimated two-year survival was 39 percent. In a separate cohort of patients with refractory metastatic colorectal cancer, estimated survival was 41 percent at two years and 33 percent at three years. The company said the consistent activity supports exploring the treatment earlier in the course of disease, such as before surgery.

The data comes from the C-800-01 trial, a multicenter Phase 1b study evaluating the combination in advanced solid tumors. The ovarian cancer cohort included patients with recurrent disease for whom no standard therapy was available or whose cancer had progressed after standard treatment. The efficacy analysis included patients who had at least one tumor scan after starting therapy, with a data cutoff of Dec. 13, 2025.

With files from Financial Post, Yahoo News and Oncodaily