PDCD4 and breast cancer: Overexpression of miR-21 has been demonstrated in multiple tumors, including glioblastoma, ovarian cancer, B-cell lymphoma, hepatocellular carcinoma, lung cancer and breast cancer and is associated with increased proliferation and invasion and decreased apoptosis (200, 201).Target genes include tumor suppressor genes, e.g. PTEN, programmed cell death 4 (PDCD4), SMAD7 and tropomyosin (TPM1).