The Phase 1b C-800-01 trial evaluated the safety and efficacy of botensilimab combined with balstilimab in 341 patients with microsatellite-stable metastatic colorectal cancer. Enrollees had immunologically cold tumors resistant to conventional checkpoint inhibitors, allowing assessment of the regimen’s ability to elicit responses in a hard-to-treat population.

Among the 341 evaluable patients, the combination therapy produced an objective response rate of 17%, with median overall survival of 17.2 months and a 24-month survival rate of 38%. These figures mark a notable improvement over historical outcomes for MSS mCRC patients.

Investigators used a novel biomarker approach balancing systemic inflammation markers against tumor immune activity to stratify patients. Data indicate that the Fc-enhanced botensilimab can overcome low baseline immune infiltration thresholds, delivering clinical benefit even in patients typically deemed unresponsive to immunotherapy.

This dataset supports further development of the BOT+BAL regimen and could broaden the eligible patient pool in upcoming Phase 2 and Phase 3 trials. Agenus plans to leverage these insights for regulatory discussions and to optimize future trial designs targeting cold tumor indications.