Expression of the c-Kit gene protein product CD117 is the most appropriate marker for GIST. c-Kit is a transmembrane glycoprotein receptor with an internal tyrosine kinase component that, when activated, triggers a cascade of intracellular signals regulating cell growth and survival. Kit mutation site has emerged as a prognostic factor of progression-free and overall survival in patients with GIST. GIST also express the hematopoietic progenitor cell marker CD34.