Gene mutations and prognostic factors analysis in extragastrointestinal stromal tumor of a Chinese three-center study.

Background: Most gastrointestinal stromal tumors (GISTs) have gain-of-function mutation of the c-kit gene, and some have mutation of the platelet-derived growth factor receptor-α (PDGFR-α) gene. Extragastrointestinal stromal tumors (EGISTs) are mesenchymal tumors that occur outside the digestive tract. But the clinicopathologic characteristics of EGISTs are still poorly understood.

Methods: Paraffin-embedded tissues from 25 cases of EGIST were analyzed for CD117, CD34, Ki-67, S-100, smooth muscle actin, and desmin expression by immunohistochemical method. These cases of EGISTs were also evaluated for the presence of c-kit exons 9, 11, 13, and 17 mutations and PDGFR-α exons 12 and 18 mutations. Survival analysis was used to evaluate the prognostic factors.

Results: c-kit mutations were detected in 44% of EGIST patients and all were exon 11 mutations. PDGFR-α mutations were found in 12% of the 25 cases and all were exon 18 mutations. Survival analysis indicated that mitotic count and Ki-67 labeling index (Ki-67 LI) were significant predictors of survival.

Conclusions: The pattern of c-kit and PDGFR-α mutation in EGISTs was essentially similar to that in GISTs. From the molecular genetics aspect, EGISTs may be a special subtype of GISTs. The results also show that the combination of mitotic counts and Ki-67 LI may be useful for predicting the prognosis of EGISTs.