The exact cause of GIST is unknown. However, we do know that there is a change in an oncogene called c-kit of almost all patients with Gastrointestinal stromal tumors. The c-kit gene is found in all cells of the body. It leads to the formation of a protein called KIT. This protein causes the cell to grow and divide. Usually the c-kit gene is inactive. It is only activated if there is a need for more interstitial cells of Cajal (ICCs). In most GISTs the c-kit gene is mutated and is always active. This may explain why the cancer forms. The cells are always growing and dividing. In families that have many members with GISTs, doctors have found inherited mutations of the c-kit gene.

In some GISTs, a different gene mutation causes the cell to make too much of a protein called PDGFRA. This has the same effect on the cell as does KIT.

These proteins (KIT and PDGFRA) act as enzymes called tyrosine kinases. These are important in the diagnosis and treatment of GIST.

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