Botensilimab plus balstilimab - (C-800-01)

July 2, 2026: Agenus Inc. (NASDAQ: AGEN) presented three-year landmark Phase 1b data at ESMO GI Congress 2026 (Munich) from the fully enrolled C-800-01 cohort (NCT03860272) evaluating botensilimab (BOT, anti–CTLA-4) plus balstilimab (BAL, anti–PD-1) in refractory microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) patients without active liver metastases (n=123; median 3 prior lines).

Efficacy: median overall survival (OS) 21.2 months; OS rates 41% at 24 months and 33% at 36 months, with a Kaplan-Meier plateau beyond two years. Confirmed objective response rate 21% (3 complete responses, 23 partial responses; 26 confirmed responses total); median duration of response not reached (range 1.9 to ≥37.4 months). Disease control rate 69% at six weeks; clinical benefit rate 28% at 24 weeks; tumor regression in >40%. At last follow-up, 21 patients (17%) were alive and off all systemic anticancer therapy (including 13 responders).

Subgroup (late-line exposed; n=37): confirmed ORR 22%, median OS 16.2 months, 3-year OS 30%; median DOR 16.6 months.

Safety: no new safety signals; no treatment-related deaths. Immune-mediated diarrhea/colitis was most common (42%; grade ≥3 15%) and resolved in 98% (median 14 days). The selected Phase 3 regimen (BOT 1 mg/kg + BAL) had lower diarrhea/colitis rates (27%; grade ≥3 10%) vs BOT 2 mg/kg.

Ongoing catalyst: continued evaluation in the randomized Phase 3 BATTMAN trial in refractory MSS/pMMR mCRC.