Gastrointestinal stromal tumor (GIST) is a disease in which abnormal cells form in the supporting connective tissues of the gastrointestinal tract – the stomach, small intestine, and large intestine. GISTs may be malignant or benign and are most common in the stomach and small intestine but may be found anywhere in or near the GI tract.
The risk of GIST is increased in people who have inherited a mutation (change) in a certain gene. In rare cases, GISTs can be found in several members of the same family. GIST may be part of a genetic syndrome, but this is rare.
Source: National Cancer Institute