<prompt> A 50 Yr. old male presents with obstructive symptoms. Biopsy of stomach reveals Gastrointestinal stromal tumor GIST. Most appropriate marker for GIST isCD 34CD 117CD 30CD 10  <response>: . GIST arises from interstitial cell of Cajal pacemaker cell which intercalates between smooth muscle cells and intramural neurons. Mutation of tyrosine kinase and platelet derived growth factor alpha PDGFa are the newer pathogenetic theories. GIST is classified as very low risk 2 cm; low risk 2-5 cm; intermediate risk 5-10 cm and high risk 10 cm based on tumour size and mitotic activity of cells. 95 of GISTS express c-kit - CD117 mutations - a specific molecular marker. ref:SRB;s manual of surgery ,ed 3,pg no 791 