A case of a protruded lesion formed by a poorly differentiated intramucosal adenocarcinoma of the stomach: an immunohistochemical analysis.

A 70-year-old woman underwent upper gastrointestinal endoscopy and was found to have a 25-mm protruded lesion in the gastric body. A biopsy revealed malignant cells. Endoscopic submucosal dissection was performed. Histopathologically, the tumor was mainly composed of poorly differentiated adenocarcinoma (PDA), while moderately differentiated adenocarcinoma was observed on its superficial layer. The tumor was located within the mucosal layer. PDAs rarely form a protruded lesion. Here, the presence of a moderately differentiated adenocarcinoma element in the superficial layer of the tumor might have protected the tumor cells from erosion, and solid proliferation of the PDA also contributed to its outward growth.