PDCD4 and cancer: Also, it has been shown that miR-21 at high expression levels stimulates cancer cell proliferation, invasion, and metastasis by downregulating many of its target genes, including Phosphatase and Tensin Homolog (PTEN), Tropomyosin 1 (TPM1), and Programmed Cell Death 4 (PDCD4), which are involved in tumor-suppressing [162].