High expression was described in 75% pancreatic ductal adenocarcinoma (PDAC), which is the most common type of PC.[46] Over expressed miR-21 was correlated with downregulation of the tumor-suppressor genes TIMP3 and PDCD4, which resulting adverse course of PDAC.[46] Additionally, miR-21 could cooperate with miR-23a and miR-21 as repressors of a network of antioncogenic genes (BTG2, NEDDRL, and PDCD4).[47] The above studies all indicated that miR-21 played an integral role in tumor pathogenesis, which made it a potential biomarker in early detection. This evidence concerns the gene PDCD4 and pachyonychia congenita.