For example, miR-122, which is highly abundant in liver, was significantly down-regulated in a large number of HCC patients, ultimately suppressing tumor invasion, proliferation and metastasis in HCC by directly binding to the 3′-UTR of the Distal-less 4 (DLX4) gene [14]; miR-21, which is markedly up-regulated in HCC, could promote tumor invasion and metastasis and accelerate tumor growth by targeting phosphatase and tensin homolog (PTEN) and programmed cell death 4 (PDCD4) [15]. The gene discussed is PDCD4; the disease is hepatocellular carcinoma.