STAT3 and hepatocellular carcinoma: Exosomes derived from hepatocellular carcinoma (HCC) cells can upregulate the expression of PD-L1 on THP-1 cells or RAW264.7 cell-differentiated macrophages, while exosomes treated with melatonin can downregulate the expression of PD-L1, which is related to regulation of the STAT3 signaling pathway [65].