Later, the intrinsic expression of PD-1 in tumor cells has also been identified in HCC [197, 198], NSCLC [199, 200], colorectal carcinomas [201, 202], Merkel cell carcinoma (MCC) [203], pancreatic cancer [204], and glioblastoma [205]. Here, PDCD1 is linked to hepatocellular carcinoma.