Gastrointestinal stromal tumor (GIST).

Gastrointestinal stromal tumors (GISTs), the most common nonepithelial neoplasms of the gastrointestinal (GI) tract, occur most commonly in the stomach. These neoplasms were previously classified as smooth muscle tumors, but it has become apparent that they represent distinct clinicopathologic entities. All GISTs should be considered as having malignant potential, although they display varying degrees of aggressiveness. Although usually asymptomatic, large GISTs may present with pain or bleeding. Definitive diagnosis is made by immunohistochemical staining of the tissue for CD117, also known as KIT protein, a cell membrane receptor with tyrosine kinase activity. Size and mitotic activity are predictive of malignant behavior. Primary treatment for GISTs with high malignant potential is surgical resection. Specific therapy targeting the KIT receptor with imatinib has resulted in improved outcomes for patients with unresectable, metastatic, and recurrent disease.