MUC4 and gastric cancer: Fourth, the current study only discussed two mucins (i.e. MUC1 and MUC2) and one pepsinogen PGC without inclusion of other mucins like MUC4 which has been reported increased expression in different types of gastric cancer like adenocarcinoma and SRCC [35] or other gastric functional proteins like pepsinogen A [36] and trefoil factors family [37-40].