'Pyloric gland-type adenoma' arising in heterotopic gastric mucosa of the duodenum, with dysplastic progression of the gastric type.

'Pyloric gland-type adenoma' is a recently described and very rare entity. We report a case of a pedunculated polyp of the duodenal bulb showing the features of pyloric gland-type adenoma. Heterotopic gastric mucosa was found adjacent to the tumour. Immunohistochemically, the tumour cells at the surface of the polyp showed foveolar-type mucin (M1) while most other tumour cells showed deep gastric mucin (M2), displaying a pattern of differentiation similar to the normal gastric mucosa. The polyp also showed villous or papillary structures with disorganization of gastric differentiation and marked increase of proliferating in foci cells. This is the first case of pyloric gland-type adenoma found to arise in heterotopic gastric mucosa of the duodenum, showing dysplastic progression of the gastric type.