PRKCI and esophageal squamous cell carcinoma: Circular protein kinase C iota (Circ-PRKCI) is a microRNA (miRNA) sponge, and it has been shown that Circ-PRKCI can participate in tumor progression by stimulating migration and proliferation of esophageal squamous cell carcinoma cells through sponging miR-3680-3p (20).