PDCD1 and colorectal cancer: Inhibition of “writers” (methyltransferase_Mettl3, Mettl14) can inhibit m6A modification, enhance the response of pMMR-MSI-L colorectal cancer patients to anti-PD-1 treatment, and significantly slow down tumor growth and prolong patient survival; activation the high expression of “readers” (signal converters_YTHDF1 and YTHDF2) may be related to the good prognosis of patients with colorectal cancer, the increase in the number of TIL, and the down-regulation of PD-L1, and may become a novel related to the immune microenvironment of colorectal cancer.