SMAD4 and prostate cancer: SMAD4 belongs to a family of signal transduction proteins that are phosphorylated and activated by transmembrane serine-threonine receptor kinases in response to transforming growth factor beta signalling via several pathways and have been reported to be biomarkers of cancers such as pancreatic cancer, juvenile polyposis syndrome, colorectal and prostate cancer, and radiation-induced lung injury [21].