CD274 and esophageal squamous cell carcinoma: Through the circ-CPA4/let-7 axis, circ-CPA4 can further enhance programmed cell death ligand 1 (PD-L1), a target of let-7 that induces cell stemness and drug resistance.[87] A similar mechanism of circRNAs as ceRNAs in promoting carcinogenesis has been found in other cancers, including breast,[88,89] colorectal,[90] endometrial cancer,[91] and esophageal squamous cell carcinomas.[92]