Assessment of 1p/19q deletions by fluorescence in situ hybridization in gliomas.

This study assessed the efficacy of FISH for detecting 1p/19q deletion in gliomas on 77 paraffin-embedded tissue samples, of which 42 cases (55%) were positive for 1p/19q codeletion; 7 of the 42 had a previous history of glioma. In one case, analysis failed. The remaining 34 cases were negative; of these, three had a previous history of glioma and one had the reverse 1q/19p deletion. A majority of the 10 recurrent gliomas had progressed, and 70% had a 1p/19q deletion. The signal pattern in a majority of 1p/19q codeletion cases was a single red marker signal and two green reference signals (1R2G) for both probe sets. One case had a different signal pattern for chromosomes 1 and 19 (1R2G and 2R4G), as seen in polysomy cells. Three cases had two target and four control signals (2R4G), as seen in tetraploid cells. Eleven had complex signal patterns seen in diploid and polyploid cells (1R2G/<nRnG). A majority of these complex cases (8 of 11, or 73%) had high-grade oligodendroglioma (n = 4) or oligoastrocytoma (n = 4). The frequency of 1p/19q combined deletion in oligodendroglioma (n = 40), oligoastrocytoma (n = 21), and astrocytoma (n = 8) was 65, 60, and 25%, respectively. Elucidated in this paper are the various FISH signal patterns observed in gliomas and a need for a uniform nomenclature for improved diagnosis.