PDCD1 and colorectal carcinoma: Another dMMR/MSI-related signature, namely, Dickkopf 1, has been reported to suppress the antitumor immune response via the glycogen synthase kinase-3β/transcription factor E2F1/T-bet axis in CD8+ T cells; this predicts poor responses to PD-1 inhibitors in patients with dMMR/MSI colorectal cancer (CRC) (21).