Combination treatment with botensilimab and balstilimab elicits durable responses in patients with refractory, metastatic, microsatellite-stable (MSS) colorectal cancer (CRC), according to a study presented at the 2023 ASCO Gastrointestinal Cancers Symposium.

Botensilimab is an Fc-enhanced CTLA-4 inhibitor, and balstilimab is a PD-1 inhibitor. Researchers tested the combination in a phase 1 trial ( Identifier: NCT03860272) of patients with refractory, metastatic, MSS CRC.

The trial included 70 patients with a median age of 57 (range, 25-83) years. More than half (57%) were women. The patients had received a median of 4 (range, 1-10) prior lines of therapy, and 59% had RAS mutations.

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Patients were treated with 1-2 mg/kg of botensilimab every 6 weeks and 3 mg/kg of balstilimab every 2 weeks. Most patients (76%) received the 2 mg/kg dose of botensilimab.

The objective response rate was 23%, which included 1 complete response and 15 partial responses. An additional 37 patients had stable disease. Among the 16 responders, 11 were still in response at the data cutoff.

The median progression-free survival was 4.1 months, and the median overall survival was not reached at a median follow-up of 7 months.

The 12-month overall survival rate was 63% overall, 81% among those without liver metastasis, and 40% among those with liver metastasis.

Most patients (91%) reported a treatment-related adverse event (TRAE). The most common TRAEs of any grade were diarrhea/colitis (43%) and fatigue (34%). The most common grade 3 TRAEs were diarrhea/colitis (20%), fatigue (4%), and pyrexia (4%).

A phase 2 trial of this combination is currently enrolling patients ( Identifier: NCT05608044), and a phase 3 trial is planned.

Disclosures: This research was supported by Agenus, Inc. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


El-Khoueiry AB, Fakih M, Gordon MS, et al. Results from a phase 1a/1b study of botensilimab (botensilimab), a novel innate/adaptive immune activator, plus balstilimab (balstilimab; anti-PD-1 antibody) in metastatic heavily pretreated microsatellite stable colorectal cancer (MSS CRC). ASCO GI 2023. January 19-21, 2023. Abstract LBA8.