miR-21, in turn, suppresses the expression of tumor suppressors such as phosphatase and tensin homolog (PTEN) [15], programmed cell death protein 4 (PDCD4) [16,17,18], reversion-inducing-cysteine-rich protein with kazal motifs (RECK), and metalloproteinase inhibitor 3 (TIMP3) by direct targeting [19]. The gene discussed is PDCD4; the disease is neoplasm.