Epithelioid gastrointestinal stromal tumor of the stomach mimicking extragastrointestinal origin.

We report a case of gastrointestinal stromal tumor (GIST) of the stomach mimicking extragastrointestinal origin. The tumor presented as a large isolated mass in the transverse mesocolon with a minor adhesion to the stomach. Microscopic examination revealed c-kit gene protein product (KIT)-positive tumor cells with epithelioid features. The tumor pseudocapsule close to the adhesion site included a small smooth muscle tissue component, indicating a gastric origin. Furthermore, tumor cells at the adhesion site showed prominent hyalinization and calcification. The tumor was diagnosed as a gastric GIST showing extensive extramural growth. Thus, GIST of the stomach and other parts of the gastrointestinal tract can present as tumors localized in the soft tissues of the abdomen mimicking extragastrointestinal origin.