CCDC66 and urinary bladder carcinoma: Recent studies point to the carcinogenesis of circRNA in many types of cancer, such as circRNA_100290 in oral cancer (26), circHIPK3 in bladder cancer (27), and circRNA CCDC66 in colon cancer (28), etc. A number of genes including circRNAs have been found to participate in ceRNA networks (29,30).