Multifocal Adenocarcinomas Arising within a Gastric Inverted Hyperplastic Polyp.

We present herein the occurrence of multifocal adenocarcinomas with a minute signet ring cell carcinoma that arose within a gastric inverted hyperplastic polyp (IHP) in a 40-year-old woman. Endoscopic ultrasonography demonstrated a heterogeneous hypoechoic mass in the third layer of the gastric wall. The endoscopic submucosal dissection specimen measuring 3.5×3.2×1.8 cm was a well-circumscribed protruding lesion that had a slit-shaped cavity. Histologically, the lesion consisted mainly of endophytic proliferation of hyperplastic columnar cells resembling normal foveolar epithelium. In addition, six foci of adenocarcinomas and a minute focus of signet ring cell carcinoma were randomly distributed in the superficial and deep regions. The adenocarcinoma was gradually transitioning from dysplasia, while the signet ring cell carcinoma was surrounded by hyperplastic foveolar epithelium. This is the first report of a gastric IHP with multifocal intramucosal adenocarcinomas and a signet ring cell carcinoma, and endoscopic submucosal dissection is used to completely resect it.