PDCD1 and cancer: Moreover, IL-6 activates the JAK-STAT3 or MEK/ERK signaling pathway to upregulate PD-L1 expression,64 and TGF-β also regulates the expression of PD-L1 in cancer cells.64 In addition to inflammatory factors, oncogenic pathways such as the epidermal growth factor receptor (EGFR), HIF-1, Myc, NF-κB, PTEN/PI3K-AKT, and mitogen-activated protein kinase (MAPK) pathways play vital roles in PD-L1 expression.65 The mechanisms by which PD-L1 expression is regulated were reviewed in another excellent review,66 and this article mainly focuses on phagocytosis and the PD-1-PD-L1 axis.