Long‐term Endoscopic Evolution of a Pyloric Gland Adenoma Arising in Nonatrophic Gastric Mucosa and Initially Resembling a Fundic Gland Polyp

ABSTRACT Pyloric gland adenoma (PGA) is a rare gastric epithelial neoplasm often associated with autoimmune or metaplastic atrophic gastritis. An 80‐year‐old man underwent serial upper gastrointestinal endoscopy. A small gastric fundus lesion initially resembling a fundic gland polyp (FGP) was followed without biopsy. Over 11 years, it enlarged to 22 mm and became increasingly whitish, against a background described endoscopically as nonatrophic. Biopsy suggested PGA, and the lesion was resected en bloc by endoscopic submucosal dissection. Closely packed pyloric‐type glands showed elongation, tortuosity, branching, and cystic dilatation, with diffuse MUC6 expression and MUC5AC expression restricted to the surface epithelium. The lesion was diagnosed as PGA with low‐grade dysplasia. The adjacent oxyntic mucosa showed no atrophy, lymphoplasmacytic infiltration, or nodular enterochromaffin‐like cell hyperplasia. Without an initial biopsy, whether the lesion was already PGA or developed within a pre‐existing FGP remains unknown. An enlarging or increasingly whitish FGP‐like lesion warrants histologic assessment, even in nonatrophic gastric mucosa.