A 50-yr-old male presents with obstructive symptoms. Biopsy of stomach reveals Gastrointestinal stromal tumor (GIST). Most appropriate marker for GIST is:

GISTs express the Kit (CD117, stem cell factor receptor) protein. The kit is a transmembrane tyrosine kinase receptor. The Kit protein is detected by immunohistochemistry and can reliably distinguish GISTs from true smooth muscle neoplasms. Most GISTs also are positive for CD34, a hematopoietic progenitor cell antigen. KIT is used not only for diagnosis but also for targeted therapy of GISTs. Imatinib, a tyrosine kinase inhibitor, is widely used in the treatment of advanced and metastatic GISTs and has been recently employed in the neoadjuvant and adjuvant set-up with encouraging results.