A gastrointestinal stromal tumor, also called a GIST, is a type of cancer that begins in the digestive system. GISTs happen most often in the stomach and small intestine.

A GIST is a growth of cells that's thought to form from nerve cells in the walls of the digestive organs. The nerve cells play a part in the process that moves food through the body.
Small GISTs may cause no symptoms. And GISTs may grow so slowly that they don't cause problems at first. As a GIST grows, it can cause symptoms that may include belly pain and nausea.

Gastrointestinal stromal tumor symptoms include:

A growth in the belly area.
Belly pain.
Fatigue.
Nausea and vomiting.
Not feeling hungry when you would expect to.
Feeling full if you eat only a small amount of food.
Dark-colored stools caused by bleeding in the digestive system.