MUC5AC was deemed to be involved in gastric carcinogenesis since gastric carcinoma was found to contain a lower level of MUC5AC expression than normal gastric mucosa [11]–[13], and several clinical studies demonstrated that MUC5AC expression level was associated with severity of GC; however, these data were inconsistent [12], [14]. This evidence concerns the gene MUC5AC and gastric carcinoma.