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Introduction: Histological classification of brain tumours, including gliomas, can be difficult, and genetic investigations are increasingly significant in their classification and the development of treatment strategies. Oligodendrogliomas often show a loss of heterozygocity for the short arm of chromosome 1 and the long arm of chromosome 19 (LOH 1p/19q), changes that influence both treatment and prognosis. Our aim was to evaluate the incidence of combined loss of heterozygocity 1p and 19q in various glioma groups. Materials and methods: A total of 10 oligodendrogliomas (5 WHO grade II and 5 grade III), 10 mixed gliomas (5 WHO grade II and 5 grade III), 10 astrocytomas (5 WHO grade II and 5 grade III) and 11 glioblastomas (WHO grade IV) were investigated. Normal hippocampal tissue was used as a control. Formalin-fixed paraffin-embedded tissue was scrutinized with fluorescent in situ hybridization (FISH) with fluorochrome-conjugated double-strand DNA probes for 1p and 19q, respectively. Results: A significiant loss of 1p/19q was found in the oligodendrogliomas; the astrocytomas showed a selective loss of 19q; the glioblastomas showed a selective loss of 1p but also polyploidy. Conclusion: This investigation confirms other reports on increased LOH 1p/19q in oligodendrogliomas. Various studies have demonstrated a large variation in the incidence of LOH 1p/19q. This might be due to inter- and intraobserver variability in the histological classification. Another factor might be variations in techniques. Most studies have been made on imprints. A standard for the method, including the number of cells counted, the cutoff limit and the statistical variation, is necessary for future studies and clinical use.

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