PDCD1 and neoplasm: In the context of anti-tumor immunotherapy, studies have shown that butyrate can enhance tumor metabolism by activating carnitine palmitoyltransferase 1A (CPT1A)-mediated Fatty Acid Oxidation(FAO),thereby suppressing CD8+ T cell activity and promoting resistance of CRC to anti-programmed cell death protein 1 (anti-PD-1).