At present, many target genes of miRNA-21 have been found, including programmed death protein 4, tropomyosin 1, homologous lost phosphatase tensin on chromosome 10, Fas ligand, tissue inhibitor of metalloproteinase-3, tumor-associated protein 63, and so on.[10,31–33] MiRNA-21 participates in a series of life activities of tumor by regulating these target genes. The gene discussed is TIMP3; the disease is neoplasm.