CD274 and hepatocellular carcinoma: Moreover, several circRNAs can affect the expression of PD-L1 through the sponge mechanism in various tumors, such as hepatocellular carcinoma (hsa_circ_0003288) [271], pancreatic cancer (hsa_circ_0046523) [272], colorectal cancer (CDR1-AS, hsa_circ_0136666, circEIF3K, has_circ_0020397) [273–276], head and neck squamous cell carcinoma (circ_0000052) [277], breast cancer (circ_0001598) [278], bladder cancer (circ_0001005) [279] and hematological system cancer (circPCBP2) [280].