Monday, April 9, 2012

Gastronintestinal Stromal Tumor (GIST)

A medical definition of a tumor is when normal cells change and grow uncontrollably. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).

A gastrointestinal stromal tumor (GIST) is a type of tumor that occurs in the gastrointestinal (GI or digestive) tract, including the esophagus, stomach, gallbladder, liver, small intestine, colon, rectum, and lining of the gut. GISTs are different from other, more common types of gastrointestinal tumors because of the type of tissue in which they start. Originally, GISTs were thought to be either muscle or nerve tumors, but recent research shows that GISTs start in cells found in the walls of the GI tract, called interstitial cells of Cajal (ICC). These cells send signals to the GI tract to help move food and liquid through the system.
GISTs belong to a group of cancers called soft tissue sarcoma. Soft tissue sarcomas are a group of cancers that develop in the tissues that support and connect the body, and the sarcoma cells resemble the cells that hold the body together, including fat cells, muscles, nerves, tendons, joints, blood vessels, or lymph vessels.
It is important to note that all GISTs can become malignant. Sometimes it may be hard for the doctor to tell immediately whether a GIST is likely to come back after treatment. As a result, the doctor will look at many factors to determine the best treatment, including the size of the tumor, whether it has already spread, how many dividing cells there are, and the tumor’s location.

Gastrointestinal stromal tumors are a group of mesenchymal neoplasms that arise from precursors of the connective-tissue cells of the gastrointestinal tract. They occur predominantly in middle-aged and older persons, and approximately 70 percent of the tumors are found in the stomach, 20 to 30 percent are found in the small intestine, and less than 10 percent are found elsewhere in the gastrointestinal tract. Recent studies have shown that cells in gastrointestinal stromal tumors express a growth factor receptor with tyrosine kinase activity termed c-kit. This receptor, the product of the proto-oncogene c-kit, can be detected by immunohistochemical staining for CD117, which appears to be the most specific diagnostic criterion for the diagnosis of gastrointestinal stromal tumors. The ligand for the c-kit receptor is stem-cell factor, also known as steel factor or c-kit ligand. Mutations of c-kit that cause constitutive activation of the tyrosine kinase function of c-kit are detectable in most gastrointestinal stromal tumors and appear to play a central part in the pathogenesis of these tumors. These mutations result in ligand-independent tyrosine kinase activity, autophosphorylation of c-kit, uncontrolled cell proliferation, and stimulation of downstream signaling pathways, including those involving phosphatidylinositol 3-kinase and mitogen-activated protein kinases. Gastrointestinal stromal tumors are notoriously unresponsive to cancer chemotherapy, and there is no effective therapy for advanced, metastatic disease.

The drug for treatment is Gleevec (which is also an oral chemo treatment for myelogenous leukemi).  Another treatment that is new is Sutent.

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