PDCD1 and melanoma: from the m6A “author” (methyltransferase_Mettl3, Mettl14) point of view, found that the deletion of methyltransferase Mettl3 and Mettl14 inhibits N6 methyladenosine (m6A) mRNA modification, enhances the response of pMMR-MSI-L colorectal cancer and melanoma patients to anti-PD-1 treatment, and significantly slows tumor growth and prolongs patient survival.