Dr Schlechter on Updated Data for Botensilimab Plus Balstilimab in MSS mCRC

“The benefit of the [combination] is maintained and the toxicity is similar across all lines of therapy, which is a novel finding, and a very important finding [with] this combination of botensilimab and balstilimab.”

Benjamin L. Schlechter, MD, of Dana-Farber Cancer Institute, discussed updated data from an expanded cohort of patients with previously treated, microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) and no active liver metastases treated with the Fc-engineered, CTLA-4 inhibitor botensilimab in combination with the anti–PD-1 antibody balstilimab during the phase 2 C-800-01 trial (NCT03860272).

At the 2025 ESMO Gastrointestinal Cancers Congress, findings from the updated analysis included 123 patients with pretreated MSS mCRC, expanding on previously published data from 77 patients. At a median follow-up of 18.0 months (range, 0.7-53.3), the overall response rate (ORR) was 20% (95% CI, 13%-28%), with a disease control rate (DCR) of 69% (95% CI, 60%-77%) at 6 weeks. Median progression-free survival (PFS) was 4.0 months (95% CI, 2.8-4.1), and the median overall survival (OS) reached 20.9 months (95% CI, 16.2-26.6). Durable benefit was further supported by a median duration of response (DOR) of 16.6 months (95% CI, 5.7-not reached). Additionally, the clinical benefit rate was 28% (95% CI, 20%-36%) at week 24.

Schlechter emphasized the consistency of clinical activity across treatment-refractory subsets, including a 37-patient fourth- or later-line subgroup lacking available standard therapies; the ORR in this group was 19% (95% CI, 8%-35%) with a median OS of 22.5 months (95% CI, 12.6-NR). Notably, efficacy outcomes were similar regardless of prior lines of therapy, underscoring the immune-driven mechanism of action of the regimen.