Immunohistological and Molecular Genetic Findings in GIST of the Stomach

Overview

The authors described immunohistological and molecular genetic findings in series of 21 tumourswith 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. Theimmunohistological profile of the third case showed that the tumour could be classified as a transitionalform between leiomyoma and GIST. All but one KIT (CD117) positive tumours were alsoCD34 positive. In other three KIT (CD117) positive cases up to 10 % of CD34 positive cells werefound. 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 indexwas not established. Risk factors were identified based on the size of the tumours and the mitoticindex. Very low and low risk of aggressive behaviour included 12 cases, intermediate risk category5 cases, high risk category 4 cases.For molecular genetic examination, DNA was extracted from formalin-fixed, paraffin-embeddedtissues. 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 pointmutation 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) andgenes than KIT gene could also trigger tyrosine-kinase activity.

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