SUMMARY
The aim. To clarify all most important immunohistochemical features of gastrointestinal stromal tumors with different histological patterns and analyze the role of expression of Ki-67, MMP-9, VEGF and p16ink4A as a predictive markers of tumor progression.Materials and methods. The study is based on analysis of 100 primary GISTs for description of their morphological features and 36 GISTs taken from this 100 for study of prognostic markers.Results. All spindle cell GISTs have shown diffuse expression of CD117 in tumor cells. The levels of CD117 expression varied from strong expression (3+) until mild expression (1+). Strong expression were seen in 75,8 % of spindle cell GISTs. Epithelioid GISTs demonstrated heterognous moderate or mild expression of CD117. All primary epithelioid GISTs from patients that had relapse of tumor in period from 1 till 3 years demonstrated focal mild expression of CD 117 in tumor cells. Expression of DOG-1 were seen in all 100 cases of GISTs, that were included in our study. The strong expression of DOG-1 (3+) were seen in all 45 GISTs that had low mitotic rate (=5 mitoses per 50HPF) and not associated with their histological pattern. GISTs with high mitotic rate demonstrated heterogeneous expression of DOG-1 in tumors: moderate expression (2+) with patchy areas of strong expression (3+). Expression of CD56 was not found in spindle cell GISTs, but single tumor cells of epithelioid GISTs that had high mitotic rate demonstrated expression of this marker. The average expression of p16ink4A were higher in tumors that gave relapses compared with tumors without relapses (50,3 % versus 5,7 % respectively, U-test=16.5; p=0,01).The average expression of MMP-9 also were significantly higher in GISTs that gave relapses: 63,2 % compared with 13,4 % in GISTs without relapse (U-test=16; p=0 ,01).The strong VEGF expression was found in 66,7 % of GISTs that had relapses and only in 8,3 % of GISTs without relapses. 50 % of GISTs without relapses was negative for VEGF. Finally, the average expression of Ki-67 were 13,4 % in GISTs with relapses and 8,7 % in GISTs without them (U-test=16; p=0,01).Conclusion. We highly recommend using DOG-1 for epithelioid GISTs. Additionally in epithelioid GISTs can be used CD56 that can give focal positive reaction in some tumour cells. The following minimal panel of markers for differential diagnosis of spindled GISTs from other mesenchymal tumors of gastrointestinal tract is proposed: CD117, DOG-1 and SMA, where the first too markers will demonstrated the moderate or strong diffuse expression and SMA can be occasionally positive in some tumor cells. p16ink4A, ki-67, VEGF and MMP-9 can be used as additional prognostic markers in GISTs.