MiR-21 targets tumor suppressor genes, such as phosphatase and tensin homolog (PTEN), tumor suppressor gene tropomyosin 1 (TPM1), programmed cell death 4 (PDCD4), maspin, and reversion-inducing cysteine-rich protein with Kazal motifs (RECK) [57–60]. The gene discussed is PDCD4; the disease is neoplasm.