General Features

GISTs may occur anywhere throughout the gastrointestinal tract, from the esophagus to the anus. They may also occur in the mesentery, omentum, and retroperitoneum. The estimated prevalence of GISTs is 10 to 20 cases per million population.10 Up to 70% of GISTs arise in the stomach and approximately 20% to 30% arise from the small bowel. Incidence in the esophagus, colon, and rectum is rare.11,12 In the esophagus, leiomyomas are more common than GIST, accounting for approximately 75% of mesenchymal tumors.13 However, in the stomach, small bowel, colon, and anorectum, GISTs account for almost all mesenchymal tumors because other tumors, such as leiomyoma and leiomyosarcoma in these sites are rare.10,14,15 Most GISTs exhibit an exophytic growth pattern, growing along the bowel wall. For small lesions, the overlying mucosa is typically intact, but mucosal ulceration may occur in large and aggressive tumors. Surrounding organ invasion may occur in approximately one-third of cases.16 Metastatic disease is common and was reported in nearly 50% of patients in one study.1 The liver is the most common site of metastases (65%), followed by the peritoneum (21%). Metastases to the lymph nodes, lungs, and bones are considered rare. Most patients eventually develop recurrence after complete surgical resection. The liver and peritoneum are the two most common sites for recurrence.17

Most GISTs are sporadic, and the majority of cases present with a solitary lesion. However, patients with type I neurofi-bromatosis have an increased prevalence of GIST. Typically, these patients are children or young adults with multiple small intestinal GISTs.18,19 Gastric GISTs may rarely occur in association with pulmonary chondromata and extraadrenal paraganglioma in Carney's syndrome,20,21 which has a predilection for young women.

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