GIST

Higher magnification of the previous image showing predominantly a spindle cell population. The vast majority of GISTs carry a mutation either in the gene for tyrosine kinase c-KIT (80% of cases) or platelet-derived growth factor receptor alpha (PDGFRA; 8% of cases). c-KIT mutation is suggested immunohistochemically as positivity for CD117. Tumors with one of these mutations may be treated with targeted therapy, such as imatinib.