MUC5AC and gastric cancer: To evaluate the expression of MUC5AC in gastric cancer, immunostaining was performed using the clinical specimen representing three-grade gastric epithelial cells from the view of tumorigenesis: non-tumorous but precancerous cells of atrophic mucosa around early gastric cancer (Fig. 1A), malignant cells of early gastric cancer endoscopically resected (Fig. 1B), and malignant cells of advanced gastric cancer surgically resected (Fig. 1C).