[A case of gastrointestinal stromal tumor of the stomach mimicking a primary tumor of the omentum minus due to the extramural growth]

We report a case of gastrointestinal stromal tumor (GIST) of the stomach mimicking a primary tumor of the omentum minus. The tumor presented as an isolated mass in the omentum minus without any adhesion to the stomach. Microscopic examination revealed that the tumor pseudocapsule on the gastric side included a small smooth muscle tissue component. The patient was given a diagnosis of a gastric GIST that showed extensive extramural growth. GISTs should not be defined by the localization of the tumor.