Immunotherapy combo shows durable survival in heavily treated ovarian cancer

A combination of two experimental immunotherapies showed a 48 percent three-year survival rate in a study of women with recurrent ovarian cancer who had received multiple prior treatments.

The results for botensilimab and balstilimab were presented Saturday at the 2026 International Gynecologic Cancer Society Annual Global Meeting in Montreal.

Among 35 patients evaluable for efficacy, the estimated three-year overall survival was 48 percent, unchanged from the two-year estimate, suggesting durable clinical benefit.

READ MORE: Income tax funds nearly half of federal spending, new tracker shows

READ MORE: Minimum wage rises in five provinces, leaving Alberta with lowest rate

"What stands out with longer follow-up is the survival plateau in patients who had already received multiple treatments," said Rebecca L. Porter, a doctor at Dana-Farber Cancer Institute who presented the data.

"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, having received a median of four prior lines of therapy, and 66 percent had received at least four.

All had previously received platinum chemotherapy, 77 percent had received bevacizumab and 57 percent had received a PARP inhibitor.

Nearly three-quarters had platinum-resistant or refractory disease, meaning their cancer had progressed during platinum treatment or returned within six months of it.

At the last follow-up, 25 percent of patients who received at least one dose of treatment (11 of 44) were alive and off all therapy.

"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 Inc., the company developing the drugs.

Responses and long-term survival were observed in both platinum-sensitive and platinum-resistant or refractory disease.

Among 25 patients with platinum-resistant or refractory disease, estimated three-year survival was 47 percent.

In 10 patients with platinum-sensitive disease, estimated three-year survival was 45 percent.

The objective response rate for all evaluable patients was 23 percent, including one complete response and seven partial responses.

Responses lasted a median of 9.7 months.

Safety remained consistent with the known profile of the drug combination, and no new safety signals or treatment-related deaths were reported.

The three-year ovarian results add to a pattern of long-term survival across difficult-to-treat cancers studied with the combination.

In the broader 400-plus patient Phase 1b pan-tumor analysis, 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 findings are notable in cancers where conventional immunotherapy has historically offered limited benefit.

The data come from the ovarian cancer cohort of the Phase 1b C-800-01 trial, which included patients with recurrent disease for whom no standard therapy was available or whose cancer had progressed after standard treatment.

The efficacy analysis included 35 patients who had at least one tumor scan after starting therapy.

The safety population included all 44 patients who received treatment.

The data cutoff for this analysis was Dec. 13, 2025.

Botensilimab and balstilimab are in development and have not been approved by the U.S. Food and Drug Administration.

With files from Financial Post, Yahoo News and Oncodaily