In this case, in addition to mucin histochemistry, the diagnosis of gastric adenocarcinoma of the pyloric gland type was made using immunohistochemistry staining for H+/K+-ATPase, a staining marker of gastric parietal cells, and pepsinogen-I, a staining marker of chief cells and mucous neck cells. The gene discussed is MUC5AC; the disease is gastric adenocarcinoma.