SMAD4 and cancer: As a signal transduction downstream effector protein in TGF-β signaling, SMAD4 (Sma Mothers Against Decapentaplegia homologue 4) or DPC4 (Deleted in Pancreatic Cancer, locus 4), is a key mediator for the response to TGFβ signal by stabilizating Smad DNA-binding complexes or recruiting transcription factors and coactivators in gene expression control [27, 28], thus leading to pleiotropic roles of TGF-β in cancer progression.