Automatized assessment of 1p36-19q13 status in gliomas by interphase FISH assay on touch imprints of frozen tumours

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Abstract
Molecular genetic analyses have demonstrated that combined losses in 1p36 and 19q13 were associated with a good response to treatment and a higher survival rates in oligodendrogliomas (O). The presence of such deletions in a subset of mixed oligoastrocytomas (OA) also suggests that 1p–19q status may assist the histological classification of gliomas. Representative frozen fragments of 25 patients with a primary grade II or III glioma [2 O, 8 astrocytic tumours (A), 15 OA] were selected and a sensitive interphase fluorescent in situ hybridization (FISH) analysis was developed on serial touch preparations using two sets of probes. A positive detection threshold at 6% was reached by the use of both touch imprints and a new set of LSI 1p36/19q13 Abbott-Vysis probes. Strong and discrete hybridization signals of these probes facilitated the following FISH analysis; indeed, an automatic analysis of the hybridization patterns (Metafer 4, Metasystems, Althlussheim, Germany) was compared with visual counting. Both methods were highly correlated and combined 1p–19q losses found in five tumours with an oligodendroglial component (2 O, 3 OA). The automatic system allowed the capture and storage of hybridization patterns and the processing of several slides. A convenient checking of the nuclei gallery was done with direct recall and visual verification on the slides of nuclei with ambiguous hybridization patterns. The recently developed probes together with automatic counting may facilitate multicentric evaluation and standardization of 1p–19q assessment in gliomas.