Extraintestinal Gastrointetsinal Stromal Tumor: Is it Biologically Different from Gastrointestinal Stromal Tumor

Extraintestinal gastrointestinal stromal tumors (EGIST) are rare tumorsoccurring at many different locations. Their clinicopathological and genotypic profile vary from the GISTs and has not been well described. Clinicopathological and genotype profiles of all EGISTs received within a period of 8 years were evaluated and compared with GIST. Genotyping for KIT and PDGFRA were done by PCR–Sanger sequencing method. Six cases of EGIST (4 mesenteric, 2 retroperitoneal) were encountered along with 74 GISTs. Four cases had epithelioidand/or mixed morphology. CD117 was positive in 100%, DOG1 in 66.7% and desmin in 50% of EGISTs. Mutation rate was 100% in EGIST and 58.8% in gastrointestinal GISTs. All EGISTs were of high malignant potential except one which was of intermediate malignant potential. Median recurrence free survival was lower in EGIST (24 months) than GIST (79 months). EGIST is distinct from the GIST by predominance of epithelioid morphology, higher malignant potential, higher desmin expression and high mutation rate thus indicating a need of specific risk stratification system for EGIST.