Endoscopic ultrasound-guided sampling of a metastatic mucinous adenocarcinoma mimicking a gastric subepithelial tumor.

Metastatic mucinous adenocarcinoma of appendix origin and mimicking a gastric subepithelial tumor (SET) is very rare. Endoscopic ultrasound (EUS)-guided sampling is a useful diagnostic method for SETs. However, the cytologic findings of metastatic mucinous adenocarcinoma are unfamiliar to many pathologists and gastroenterologists. These findings present a diagnostic challenge because the introduction of gastric epithelium and mucin into the specimen during the procedure can be misleading. This is the first reported experience of an EUS-guided sampling of a gastric SET in a patient with suspected appendiceal tumor, to make the diagnosis of a mucinous adenocarcinoma.