Agenus Announces New Findings From Long-Term Survivor Analysis Of Phase 1b C-800-01 Trial Evaluating Botensilimab In Combination With Balstilimab In Heavily Pretreated Patients With MSS, mCRC Without Active Liver Metastases

• Long-term survival of patients in the 123-patient Phase 1b CRC cohort was not limited to patients with favorable baseline characteristics, suggesting durable benefit may extend across a broader patient population
• Approximately 1 in 4 long-term survivors were alive and off all cancer therapy at last follow-up, with responses lasting more than three years
• Patients with fewer prior lines of treatment were more likely to achieve long-term survival, supporting rationale for BOT+BAL earlier in the course of treatment

Agenus Inc. (NASDAQ:AGEN), a leader in immuno-oncology innovation, today announced new findings from a long-term survivor analysis of its Phase 1b C-800-01 trial evaluating botensilimab (BOT), a multifunctional, Fc-enhanced anti-CTLA-4 antibody, in combination with balstilimab (BAL), an anti-PD-1 antibody, in heavily pretreated patients with microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) without active liver metastases. The results were presented in a poster by Thomas U. Marron, MD, PhD, of the Tisch Cancer Center at Mount Sinai, at the Society for Immunotherapy of Cancer (SITC) 2026 Annual Meeting in Phoenix, Arizona.

For patients with MSS mCRC whose cancer has progressed despite multiple treatments, treatment options remain limited, even among patients without active liver metastases. Historical studies of available later-line treatment regimens have reported median overall survival of approximately 10–14 months in relevant populations.1,2 Because survival beyond 18 months remains uncommon in this setting, the analysis defined long-term survivors as patients who lived at least 18 months after starting BOT+BAL.

The new SITC analysis builds on previously reported results from the full 123-patient cohort, which demonstrated median overall survival of 21.2 months and a 33% estimated three-year survival rate, as presented at ESMO GI 2026 and published in Clinical Cancer Research. The current post-hoc analysis takes a closer look at the patients who achieved long-term survival, examining their clinical characteristics, the durability of their responses and factors that may help explain their outcomes.

The analysis found that 51% (63/123) of patients survived at least 18 months after starting BOT+BAL, including patients who had received prior immunotherapy and undergone several rounds of different treatment. Among the 63 long-term survivors, median overall survival had not been reached and an estimated 59% were alive at three years.