Gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors characterized by a spindle morphology and expression of the c-kit proto-oncogene. They occur primarily in the stomach and small intestine presenting with abdominal pain or bleeding, but may be found incidentally. These tumors may behave malignantly by metastasizing, invading adjacent organs, or recurring after resection. Tumor size more than 5 cm or more than 5 mitoses per high-power field (HPF) are most useful inpredicting subsequent malignant behavior. Endoscopy generally reveals a submucosal tumor that may have a central umbilication or ulcer. Endoscopic forceps biopsies are usually nondiagnostic. Endoscopic ultrasound (EUS) reveals a hypoechoic mass generally arising from the fourth endosonographic layer (muscularis propria). EUS-guided fine-needle aspiration (FNA) with staining of the specimen for the c-kit protein (CD-117) and CD-34 can establish the diagnosis. The treatment of choice is complete surgical resection for all tumors that have malignant features. Controversy surrounds whether small benign-appearing GISTs require resection. Patients with unresectable, metastatic and/or recurrent GISTs may be treated with the tyrosine kinase inhibitor imatinib mesylate with 80% of patients either responding or having stable disease.