MUC5AC and gastric cancer: In our previous study, REG4 mRNA and protein expression levels were found to be increased in gastric intestinal metaplasia compared to those in gastric cancer and normal mucosa; higher serum REG4 levels were observed in patients with gastric cancer compared to healthy individuals; and REG4 was expressed more frequently in signet ring cell carcinoma, which closely correlated with MUC-2, and MUC-5 AC expression [13].