Gastric intramucosal adenocarcinoma with an invasive micropapillary carcinoma component.

A 70-year-old woman was referred to our hospital because of early gastric cancer (lesser curvature of the antrum, 0-IIc, tub1, 15 mm) and underwent endoscopic submucosal dissection. Microscopically, the lesion was found to be confined to the mucosa, and predominantly composed of well-differentiated tubular adenocarcinoma with a micropapillary component. On immunohistochemical examination, the characteristic "inside-out pattern" of the micropapillary component was observed; thus, we diagnosed the lesion as gastric cancer with a micropapillary component. Invasive micropapillary carcinoma is a rare subtype of gastric carcinoma, and, to our knowledge, this is the first case of invasive micropapillary carcinoma of the stomach confined to the mucosa.