Gastrointestinal stromal tumors. A review of characteristics morphologic, immunohistochemical, and molecular genetic features.

Gastrointestinal stromal tumors are a heterogeneous group of neoplasms composed of either spindled or epithelioid cells that have distinctive histologic appearances and clinical behaviors in different portions of the gastrointestinal tract. These tumors are best evaluated in a site-specific manner, and prediction of clinical behavior is best achieved by evaluation of multiple characteristics, including cell type, cellularity, nuclear pleomorphism, mitotic counts, and the presence or absence of mucosal invasion and tumor cell necrosis. The vast majority of these tumors can be reliably placed into benign or malignant categories using a constellation of morphologic features. Almost two thirds of these tumors arise in the stomach, and slightly less than one third occur in the small bowel. The remaining tumors arise (in descending order of frequency) in the anorectum, large bowel, and esophagus. These tumors uniformly express CD117, and mutations of the c-kit gene are central to their pathogenesis and likely the key to effective therapeutic intervention.