PDCD1 and hepatocellular carcinoma: Targeting regulators like METTL3, METTL14, the IGF2BP family, ALKBH5, or FTO can enhance the efficacy of PD-1 blockade therapy in renal clear cell carcinoma, colorectal cancer, melanoma, NSCLC, breast cancer, hepatocellular carcinoma, and intrahepatic cholangiocarcinoma.