SMAD7 and digestive system cancer: Cancer cell lines originating from same organ often gathered in the same cluster, such as C2 [COAD/READ-STAD-PAAD], a group of digestive system cancers whose common features were the high expression of CNKSR1, FOLH1, ADGRG1, SMAD7, LRATD1 and MVP (Haffner et al., 2009; Ji et al., 2018; Kobayashi et al., 2006; Quadri et al., 2017; Slattery et al., 2010; Teng et al., 2017).