Poorly differentiated adenocarcinoma with signet-ring cell carcinoma in a hyperplastic polyp of the stomach: report of a case.

Hyperplastic polyps (HPs) of the stomach have been reported to be mostly benign. However, in rare cases, carcinomas have been found in HPs. We treated a 59-year-old Japanese male who underwent a total gastrectomy, and a gross examination of the resected stomach revealed a 4.8 x 3.8-cm polyp on the greater curvature of the antrum and multiple small polyps in the whole gastric mucosa. Histologically, the large polyp consisted mainly of hyperplastic foveolar epithelium, while the presence of variously colored lobules demonstrated a poorly differentiated adenocarcinoma mixed with signet-ring cell carcinoma. Hyperplastic polyps should therefore be carefully examined microscopically as a polypectomy specimen and in resected stomach specimens.