The role of miR-21 in tumorigenesis has been extensively studied in cancer cells, revealing its regulatory roles in various downstream signaling pathways associated with cell proliferation 7, migration 8, 9, apoptosis 10, and chemoresistance via suppression of pro-apoptotic protein expression, including phosphatase and tensin homolog (PTEN) and programmed cell death protein 4 (PDCD4). The gene discussed is PDCD4; the disease is cancer.