CTLA4 and cancer: A single arm non-randomized multi-cohort clinical trial in patients with advanced dMMR/MSI-H colorectal cancer has similarly suggested superiority of combined anti-PD-1/CTLA-4 blockade using nivolumab and ipilimumab compared to nivolumab monotherapy.7 Additionally, there is limited evidence that combined anti-PD-1/CTLA-4 blockade can overcome resistance in patients with MSI-H malignancies who progress on anti-PD-1 monotherapy.8,9