The combination therapy of botensilimab plus balstilimab resulted in encouraging anti-tumor activity in heavily pre-treated patients with microsatellite stable colorectal cancer (MSS CRC) in a phase 1a/1b trial. According to the investigators, the safety profile of this treatment regimen was manageable.

The phase 1a/1b C-800 study is the first in-human trial to combine botensilimab plus balstilimab in patients with advanced cancer.1 Patients with refractory metastatic MSS CRC received 1 or 2 mg/kg of the Fc-enhanced CTLA-4 inhibitor botensilimab, every 6 weeks, and 3 mg/kg of the PD-1 inhibitor, every 2 weeks. Prof. Anthony El-Khoueiry (Norris Comprehensive Cancer Center) presented the results at ASCO-GI 2023.

The overall response rate was 23%, mostly comprised by partial responses (21%). In addition, the stable disease rate was 53%, resulting in a disease control rate of 76%. The median progression-free survival was 4.1 months, and the median overall survival had not been reached at the time of the presentation. According to Prof. El-Khoueiry, the safety profile of the combination therapy was manageable. Any grade treatment-related adverse events were seen in 91% of patients, and grade 3 or 4 events were observed in 32% and 2% of patients, respectively.

The promising anti-tumor activity and manageable safety profile of the combination therapy of botensilimab and balstilimab in this phase 1a/1b trial instigated further investigation of this regimen in patients with MSS CRC in phase 2 and phase 3 studies.

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