A gastrointestinal stromal tumor (GIST) is a mesenchymal neoplasm most commonly seen in the gastrointestinal (GI) tract. It represents 1% of all malignancies. Most GISTs express the KIT (CD117) immunohistochemical marker. Extra-gastrointestinal stromal tumors are rare and have been described to involve the central nervous system, omentum, or peritoneum.

Extraintestinal GISTs have histologic and immunohistochemical features identical to those of GISTs. While abdominal pain, anorexia, and GI bleeding are common presenting symptoms when GISTs occur within the GI tract, there are no specific presenting symptoms for extra-intestinal GISTs. Typically, symptoms relate to the affected part / system of the body.

Extraintestinal GISTs are most common in individuals of Northern European descent, occur equally in men and women, and have peak incidence in the fourth to sixth decades of life. Given the rarity of extraintestinal GISTs, prognosis and incidence have yet to be defined.