<prompt> True about GIST all exceptMost common in duodenumNecrosis and ulceration presentPET is used to assess response to therapyWell circumscribed  <response>: .GIST Gastrointestinal stromal tumour is rare but most common non epithelial small bowel tumours. 25 of GIST occurs in small bowel stomach - 50 to 60. It is 0.2 of all GI tumours. It is equal in both sexes It arises from interstitial cell of Cajal. More than 95 show c-kit transmembrane receptor tyrosine kinase mutation. Many mesenchymal tumours of small bowel are now classified as GIST. GIST attains massive size when presenting clinically. Palpable mass, compression, haemorrhage are the features. CT is diagnostic. ref:SRB;s manual of surgery,ed 3,pg no 812 