What is a Gastrointestinal Stromal Tumor? and Other Questions About GIST
The gastrointestinal tract is a system of linking tubes that extend from the mouth to the anus. This tract, also known as the digestive tract or the GI tract, uses muscle contractions in combination with the release of hormones and enzymes to digest food. In addition to digesting food, the GI tract also processes food for energy and rids the body of solid waste. The gastrointestinal tract begins in the mouth and then proceeds to the esophagus, the stomach, the duodenum, the small intestine, the large intestine (colon), the rectum, and the anus.
Gastrointestinal Stromal Tumors are believed to initially form in the cells in the GI tract wall. These special cells are called interstitial cells of Cajal (ICCs). These ICCs are part of the autonomic nervous system and sends signals to the gastrointestinal tract. These signals cause the digestive tract muscles to contract, therefore moving food and liquid through the digestive system.
Most gastrointestinal stromal tumors form in the stomach and the small intestine; however, a smaller percentage of GISTs develop in other areas of the GI tract. GISTs are difficult to diagnose due to the fact that they "hide" in the GI tract and often times do not cause any physical symptoms.
In recent years, doctors have made great progress in learning how changes in DNA can cause normal cells to become cancerous. For some cancer types, these changes in DNA are inherited. In other cancer types, like GISTs, changes occur for no apparent reason. Though doctors are not exactly sure what causes gastrointestinal stromal tumors, doctors have discovered that almost all patients with GISTs have an altered c-kit oncogene. This gene is found in almost all cells in the body. The c-kit gene is responsible for the formation of the KIT protein which causes cells to grow and divide. The c-kit gene is usually inactive and is only activated if there is a need for more ICCs. In those who have GISTs, a mutation causes the c-kit gene to remain active. This causes an abundance of ICCs which explains why the cancer forms. Another protein called PDGFRA is caused by a different gene mutation but has the same effect as the KIT protein. Both KIT and PDGFRA act as enzymes called tyrosine kinases. These enzymes are very important for the diagnosis and treatment of gastrointestinal stromal tumors.