Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. GISTs arise in the smooth muscle pacemaker interstitial cell of Cajal, or similar cells. They are defined as tumors whose behavior is driven by mutations in the KIT gene (85%),  PDGFRA gene (10%), or BRAF kinase (rare). 95% of GISTs  stain positively for KIT (CD117). Most (66%) occur in the stomach and gastric GISTs have a lower malignant potential than tumors found elsewhere in the GI tract. Classification
GIST was introduced as a diagnostic term in 1983.: 1060  Until the late 1990s, many non-epithelial tumors of the gastrointestinal tract were called "gastrointestinal stromal tumors". Histopathologists were unable to specifically distinguish among types we now know to be dissimilar molecularly. Subsequently, CD34, and later CD117 were identified as markers that could distinguish the various types. Additionally, in the absence of specific therapy, the diagnostic categorization had only a limited influence on prognosis and therapy. The understanding of GIST biology changed significantly with identification of the molecular basis of GIST,: 1065  particularly c-KIT. Historically, literature reviews prior to the molecular definition of GIST, and for a short time thereafter, asserted that 70-80% of GISTs were benign. The identification of a molecular basis for GIST led to the exclusion of many tumors that had been considered as GIST previously, and also the incorporation of a much larger number of tumors that had been labeled as other types of sarcomas and undifferentiated carcinomas.
Prednicarbate is a relatively new topical corticosteroid drug. It is similar in potency to hydrocortisone. Corticosteroids have always been an important part of the pharmacological arsenal of dermatology; however, their tendency to produce side-effects has caused the need to search for new preparations.It is nonhalogenated. == References ==