SMAD4 and neoplasm: The molecular function of miR-224 has been studied recently, and a growing body of evidence has shown that miR-224 regulates tumor proliferation through several signal transduction pathways, such as cell cycle progression [22] and NF-κB and TGF-β signaling pathways [23, 24], through direct interactions with various tumor-related genes including PHLPP1 and PHLPP2 in colorectal cancer [20], SMAD4 and TNFAIP1 in NSLC [25], and TPD52 in prostate cancer [21].