Gastrointestinal stromal tumours (GIST) occur most often in either the stomach or the small intestine, but they can occur in any part of the digestive tract, or in the lining and supportive tissues of the belly (the peritoneum and the mesentery).

The behaviour of GISTs is quite variable. Some are quite benign (non-cancerous), whilst others behave more like cancers, invading nearby organs and sending seedlings of tumour to the liver or the peritoneum (the lining of the belly).

The cause of GISTs is not known. The usual symptoms are either pain or bleeding into the digestive tract.

The treatment of GISTs is surgery to remove the tumour with a good margin of normal tissue, to reduce the risk of the growth coming back. Even so there is quite a tendency for these growths to come back months or years after the operation.

Until recently the treatment of more advanced GISTs that had spread too far for surgery to be possible had been difficult since normal chemotherapy drugs were not very effective. But a new drug, called imatinib (Glivec®) is very active against GISTs.