<prompt> Most common site of GIST is -IleumEsophagusColonStomach  <response>: Ans. is d i.e., Stomach Gastrointestinal stromal tumors GlSTso GISTs are the most common mesenchymal neoplasm of gastrointestinal tumor.o GIST represents a distinct group of gastrointestinal tumors that originate from the interstial cells of cajal which control gastrointestinal peristalsis.o GISTs can occur anywhere in the gastroinstestinal tract; the most common site being the stomach followed by small intestine.Stomach-50-70Small intestine -20-30Colon rectum-5-15Esophagus -5 Immunohistochemistrvo Following markers are present in GISTs:i CD 117 c kit- 95ii CD 34-70iii Smooth muscle actin- 5o CD 117 c kit is considered the most specific markero CD 117 c kit immunoreactivity is the best defining feature of GISTs distinguishing them from true smooth muscle tumors leiomyoma and tumors arising from neural crest.o Although CD 117 c kit is considered the most specific marker for GIST, it is not pathognomonic of GIST as other tumors may also express CD 117. These tumors include mast cell tumor, germ cell tumors seminomas, leukemias, malignant melanoma, angiolipomas, and some sarcomas.o Gastrointestinal stromal tumors GIST originate from the interstitial cells of Cajal. 