ABSTRACT
Objective To evaluate prognostic significance of c-kit and PDGFR-α gene mutation in extragastrointestinal stromal tumors(EGIST). Methods Paraffin embedded tissue specimens from 23 EGISTs were tested for CD117,CD34 and Ki-67 expression by immunohistochemical method.EGIST cases were also tested for the presence of c-kit exons 9,11,13,17 mutations and PDGFR-α exons 12,18 mutations.Kaplan-meier survival rate was used to evaluate the prognostic factors. Results Of 23 cases of EGIST,23(100%)were positive for CD117,17(74%)were positive for CD34.For Ki-67 labeling index(Ki-67 LI):30%were＜1%,44%were between 1%-5%,26%were＞5%.C-kit mutations were detected in 44% of EGIST patients and all were of exon 11 mutations.PDGFR-α mutations were found in 13%of all the 23 cases and all were of exon 18 mutations(The commonest type of mutation D842V).Survival analysis indicated that mitotic count and Ki-67 index were significant predictors for survival.Conclusion The pattern of c-kit and PDGFR-α mutation in EGIST was essentially similar to that in GIST.But the mutation frequency of PDGFR-α was slightly higher in EGIST than in GIST.EGIST could be a special subtype of GIST.The results of this study also show combination of mitotic counts and Ki-67 labeling index may be useful for predicting the prognosis of EGIST.