Trial results for a Phase 2 study investigating botensilimab in combination with balstilimab for colorectal neoplasms were posted on ClinicalTrials.gov on 2026-05-22. The study reported a 100% composite rate of clinical complete response or major pathological response in Cohort C at 6 months.
Background
The study explored the combination of botensilimab, a cytotoxic T lymphocyte-associated protein 4 (CTLA-4) inhibitor, and balstilimab, a programmed cell death protein 1 (PD-1) inhibitor. This immunotherapy combination was investigated in participants with colorectal cancer before surgical tumor removal to assess its effects and side effects.
Trial design
The Phase 2 pilot study (NCT05571293) enrolled 26 participants with colorectal neoplasms across three cohorts. It investigated whether the combination of botensilimab and balstilimab could be administered to patients with colorectal cancer prior to surgical tumor removal, assessing side effects and their effect on the cancer. Participants in Cohort A received a total of 2 doses of balstilimab.
Key results
The trial results included several key measurements:
- For Pathological Overall Response (pOR) Rate, 7 participants were reported in Cohort A (Botensilimab and Balstilimab) and 8 participants in Cohort B.
- In Cohort C, the composite rate of clinical complete response or major pathological response at 6 months was 100 percentage of patients.
- Regarding safety, 2 participants in Cohort A experienced potentially treatment-related serious adverse events (SAEs) according to the Common Terminology Criteria for Adverse Events (CTCAE) v5.0 at 90 days following the last treatment.
- 0 participants in Cohort A experienced treatment-related complications leading to delays of 12 weeks or more in surgery after treatment initiation.
- Changes in minimal residual disease (MRD) assessed using ctDNA pre-surgical resection showed:
- Cohort A: Mean 0.42 MTM/ml (Standard Deviation 0.355), Median 0.42 MTM/ml.
- Cohort B: Mean 15.77 MTM/ml (Standard Deviation 4.35).
- Cohort C: Mean 5.7 MTM/ml.
- Changes in minimal residual disease (MRD) assessed using ctDNA 30 days post-surgical resection showed:
- Cohort A: Mean 0.00 MTM/ml (Standard Deviation 0.00).
- Cohort B: Mean 0.00 MTM/ml (Standard Deviation 0.00).
- Cohort C: Mean 0.00 MTM/ml (Standard Deviation 0.00).
What this means
The reported 100% composite rate of clinical complete response or major pathological response in Cohort C suggests a strong initial signal for the combination of botensilimab and balstilimab in colorectal cancer. The pathological overall response rates in Cohorts A and B, along with the low number of SAEs and zero surgical delays in Cohort A, indicate a potentially manageable safety profile in the pre-surgical setting. The reduction of minimal residual disease to 0.00 MTM/ml post-surgery across all cohorts, as measured by ctDNA, is a notable finding that could suggest effective tumor clearance or reduction following treatment and surgery. These early Phase 2 results warrant further investigation in larger trials to confirm efficacy and long-term outcomes for patients with colorectal neoplasms.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for the study NCT05571293, titled "Combination Immunotherapy in Colorectal Cancer", were posted on 2026-05-22 on clinicaltrials.gov.