PDCD1 and colorectal carcinoma: CRC with dMMR/MSI-H have high TMB and often have high immune infiltrates.36 37 In the clinic, monotherapy with anti-PD-1 monoclonal antibodies (mAbs), pembrolizumab and nivolumab, and combination therapy of nivolumab with the anti-CTLA-4 mAb, ipilimumab, have been approved for patients with CRC with dMMR who have progressed after treatment with first-line chemotherapy.38 However, only a very small subset of patients with CRC could benefit from ICI since only a small percentage of the CRC patient population has the dMMR phenotype.