Gastrointestinal stromal tumors (GISTs) are cancerous (malignant) tumors that develop from a specific kind of cell (mesenchymal precursor cells) within the wall of the esophagus, stomach, or intestines. Most gastrointestinal stromal tumors are caused by a mutation in a gene called C-KIT that controls the growth of cells. Most (60 to 70%) of these tumors occur in the stomach, 20 to 25% occur in the small intestine, and a small percentage occurs in the esophagus, colon, and rectum.
The average age at diagnosis is 50 to 60. People who have had radiation therapy to the abdomen for the treatment of other tumors can develop gastrointestinal stromal tumors at a later time. These tumors usually grow slowly, but some can grow more rapidly and spread to other sites (metastasize).
A doctor may use an endoscope or colonoscope (a flexible viewing tube—see Endoscopy) to locate the tumor and do a biopsy (remove a tissue sample for examination under a microscope). A wireless battery-powered capsule that contains one or two small cameras (see Video Capsule Endoscopy) can also be used to show tumors of the small intestine, but this technique does not allow the doctor to do a biopsy.