PDCD1 and neoplasm: However, in the case of malignant tumors, upregulation of PD-L1 expression occurs due to factors such as high expression of MYC, EGFR, activation of the PI3K/AKT/mTOR signaling pathway, and the Ras/Raf/MEK/MAPK-ERK signaling pathway, leading to the interaction between PD-1 and its ligands PD-L1/PD-L2, thereby blocking the activation of immune cells, impairing T cells function, and serving as one of the main mechanisms by which tumor cells evade anti-tumor immunity 18-20.