Molecular cytogenetic stratification of recurrent oligodendrogliomas: utility of interphase fluorescence in situ hybridization (I-FISH)

In oligodendroglial brain tumours, losses of chromosomal material of the short arm of chromosome 1 and long arm of chromosome 19 have been shown to predict responsiveness to chemotherapy and prolonged patients' survival. Therefore, the correct diagnosis of these genetic alterations in tumours of oligodendroglial origin is particularly important. To detect deletions of 1p36 and/or 19q13.3 in oligodendroglial cells we used dual-colour I-FISH with locus-specific DNA probes. I-FISH was performed on isolated whole cell nuclei, prepared from fresh non-fixed tumour tissue samples resuspended in media and processed using a standard cytogenetic procedure, thus bypassing the problem of nuclear truncation. We examined 16 patients with histologically proved oligodendrogliomas (5x oligodendroglioma, 9x anaplastic oligodendroglioma, 2x anaplastic oligoastrocytoma). The results of molecular cytogenetic analyses were correlated with morphological and clinical findings. Molecular cytogenetic analyses were successful in 15 patients and, due to a non-adequate tissue specimen, were uninformative in one patient only. Combined deletions 1p36/19q13 were proved in 13 patients. However, in six of them additional genetic alterations typical for high-grade astrocytoma were found, which could have negative influence on the prognosis. One patient had isolated deletion of 1p36 and another had a normal genetic pattern without any chromosomal alterations. In summary, I-FISH on isolated cell nuclei is a powerful tool for detecting chromosomal aberrations in tumour cells. A systematic molecular cytogenetic analysis may advance diagnosis, prognostic stratification, and targeted treatment of patients with brain tumours.