MiR-21 is upregulated in HCC cells and tissues, which are associated with the capacity of cancer cell migration and invasion in HCC, where the miR-21 expression is inversely correlated with the protein expression of its targeted gene, programmed cell death 4 (PDCD4), and signaling molecules of its downstream pathway [103]. The gene discussed is PDCD4; the disease is hepatocellular carcinoma.