Agenus has reported 48% estimated three-year overall survival with botensilimab plus balstilimab in an early-phase recurrent ovarian cancer cohort. Presented at the 2026 International Gynecologic Cancer Society (IGCS) Annual Global Meeting in Montréal, the findings included patients whose disease had become resistant or refractory to platinum chemotherapy.
The survival estimate remained unchanged between years two and three, drawing attention to the possibility of lasting benefit for a subset of patients.
Rebecca L. Porter, MD, of Dana-Farber Cancer Institute, who presented the findings, said:
“What stands out with longer follow-up is the survival plateau in patients who had already received multiple treatments.”
Steven J. O’Day, MD, Chief Medical Officer of Agenus, highlighted the survival curve extending beyond two years in women who had received multiple previous treatments, including those with platinum-resistant or refractory disease. He noted that a similar pattern of durable survival had been observed in other difficult-to-treat cancers studied with botensilimab plus balstilimab.
“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.”
Three-Year Survival and Tumor Responses
Among 35 efficacy-evaluable patients, estimated three-year overall survival was 48%, while median overall survival was 14.8 months. The objective response rate reached 23%, comprising one complete response and seven partial responses. Responses lasted a median of 9.7 months, and 31% experienced a response or stable disease lasting at least 24 weeks.
At last follow-up, 11 of all 44 treated patients were alive and off all therapy.
Activity in Platinum-Resistant or Refractory Disease
Patients had received a median of four previous treatment lines. Among 25 efficacy-evaluable patients with platinum-resistant or refractory disease, estimated three-year survival was 47%, with a 20% response rate. In 10 patients with platinum-sensitive disease, the corresponding results were 45% and 30%.
These small subgroup analyses are exploratory. They cannot establish whether platinum sensitivity predicts benefit from the combination or support reliable comparisons between the groups.
How Botensilimab and Balstilimab Work
The combination pairs two investigational immune checkpoint antibodies. Botensilimab targets CTLA-4 and incorporates an enhanced Fc region, the part of an antibody that interacts with other immune cells. Balstilimab targets PD-1.
Botensilimab is designed to strengthen antitumor immune activity through several mechanisms, including T-cell activation, modulation of intratumoral regulatory T cells, and activation of myeloid cells. The approach is being investigated in cancers that have responded poorly to conventional checkpoint inhibition.
What the Findings Mean
The ovarian cohort forms part of the multicenter Phase 1b C-800-01 trial (NCT03860272). The published ovarian study describes safety and tolerability as its primary objectives, alongside assessments of tumor response, response duration, and progression-free survival.
The survival plateau is a signal worth investigating, but this small cohort does not establish a survival advantage over standard treatment. Overall survival also differs from remaining free of cancer progression: the three-year estimate should not be interpreted as a cure rate.
Agenus reported no new safety signals or treatment-related deaths in the update. Neither botensilimab nor balstilimab is approved by the U.S. Food and Drug Administration.
For recurrent ovarian cancer, the findings support further research into whether this immunotherapy combination can produce durable benefit, and which patients are most likely to experience it.
Read further on OncoDaily: BOT/BAL in MSS Metastatic Colorectal Cancer Without Active Liver Metastases
