MUC1 and gastric cancer: There are many immunohistochemical studies on MUC1 expression in GC, and most of them reported MUC1 staining in roughly more than 50% of both IGC and DGC except for signet-ring cell carcinoma, a poorly differentiated GC in which the MUC1 expression was observed only 10% (Table 2) [38–46].