SMAD4 and gastric cancer: Examples of such escape include the mutation of SMAD4 in pancreatic ductal adenocarcinoma (PDAC) and gastric cancer (GC) [110, 111], the TβR I mutation in colon cancer [112], and even mutations in genes that encode TGF-β ligands (BMP5), receptors (TβR II, AVCR2A, BMPR2), and SMADs (SMAD2 and SMAD4) [113, 114].