<prompt> All are true about GIST EXCEPT?Most common mesenchymal tumor of GITC-kit CD 117 positiveOriginate from interstitial cells of CajalMajority seen in duodenum  <response>: Ref: Robbins Pathology, 9th ed. pg. 775-76 Majority of gastrointestinal stromal tumors originate from stomach. The cell of origin is interstitial cell of Cajal which are present in muscularispropria. The useful marker is c-kit CD 117 detectable in 95 of patients. PET scan is the imaging modality of choice Treatment is tyrosine kinase inhibitors like imatinib mesylate. 