PDCD4 and esophageal squamous cell carcinoma: It has previously been demonstrated that miRNAs play an important role in tumor initiation and progression.[13] In ESCC, miR-375 is frequently downregulated in cancer cells and functions as a tumor suppressor.[14] MiR-183 might play an oncogenic role in suppressing apoptosis and promoting proliferation in ESCC by regulating the PDCD4 expression.[15] It is known that miR-21 acts as an oncogenic miRNA in several types of cancer.