The authors described immunohistological and molecular genetic findings in series of 21 tumours with spindle and epithelioid cells histology of the stomach. In 18 cases the tumours were KIT (CD117) positive and the diagnosis of gastrointestinal stromal tumour (GIST) was confirmed. Three cases were KIT (CD117) negative. According to additional immunohistological markers (desmin and smooth muscle actin positivity) two of them were categorized as leiomyomas. The immunohistological profile of the third case showed that the tumour could be classified as a transitional form between leiomyoma and GIST. All but one KIT (CD117) positive tumours were also CD34 positive. In other three KIT (CD117) positive cases up to 10 % of CD34 positive cells were found. Desmin was negative in KIT (CD117) positive cases. S100 protein was positive in three KIT (CD117) positive cases ranging from single cells to 10 % of cells. Nine tumours were NSE positive. In our study the connection between proliferation factors (Ki67 and PCNA) and the mitotic index was not established. Risk factors were identified based on the size of the tumours and the mitotic index. Very low and low risk of aggressive behaviour included 12 cases, intermediate risk category 5 cases, high risk category 4 cases. For molecular genetic examination, DNA was extracted from formalin-fixed, paraffin-embedded tissues. Exon 11 was analyzed by SSCP (single-strand conformational polymorphism analysis) with following sequencing. Deletion was found in 7 cases, point mutation in one case, silent point mutation in one case and in two cases the examination could not be detected. In 10 cases (47 %) a „wild type“ was found. We suggest that other exons, e.g. 9, 13, 17, (which were not examined) and genes than KIT gene could also trigger tyrosine-kinase activity.

        Key words: gastrointestinal stromal tumours – immunohistology – molecular genetic examination