Cytogenetic analysis of gliomas by in situ hybridization of stereotactic biopsy material

Cytogenetic analysis of gemistocytic cells in gliomas

Gemistocytes are glial cells characterized by voluminous, eosinophilic cytoplasm and a peripherally positioned, often flattened nucleus. Gemistocytes, usually present in anoxic-ischemic brains, are regularly encountered in glial neoplasms. The presence of gemistocytes in gliomas has been associated with an unfavorable clinical course, notwithstanding the low proliferative potential of these cells. It is not known whether gemistocytes residing in gliomas are dormant tumor cells, or alternatively, represent interspersed reactive glial cells. Whereas gemistocytic astrocytomas have been subject to various genetic investigations, no genomic analysis comparing individual cells in gliomas has been reported so far. In the present study, 3 astrocytomas, 3 oligodendrogliomas, and 3 mixed oligoastrocytomas, all harboring gemistocytic cells, were genetically analyzed by DNA in situ hybridization to paraffin-embedded, formalin-fixed tissue samples with optimal preservation of cellular morphology. To this end, probes for the centromeric regions of chromosome 7 and 10, known to show copy number aberrations in gliomas, were used. In addition, probes for centromeric regions of chromosomes 1 and 17 were used for the ploidy status of the tumors. The spot counts for the various chromosomes were statistically compared. Gains of chromosome 7 were found in 1 anaplastic astrocytoma, 1 anaplastic oligodendroglioma, and 1 anaplastic oligoastrocytoma. Loss of chromosome 10 was seen in 2 anaplastic astrocytomas, in 1 anaplastic oligodendroglioma, and in 1 anaplastic oligoastrocytoma. In 3 cases, significant differences in spot distributions between gemistocytes and non-gemistocytes were found, but the other cases showed no difference in spot distribution. It is concluded that, although many gemistocytic cells in gliomas may be considered reactive cells, in a subset of tumors, part of the gemistocytic cells should be considered neoplastic.

Non-isotopic molecular cytogenetics in neuro-oncology

The molecular genetic analysis of brain tumours has been the focus of considerable interest for a number of years. However, these studies have been largely directed towards understanding the fundamental biological processes involved in tumorigenesis and the techniques which have been used require considerable molecular biological skills. Unfortunately, there has not been the impetus to correlate basic biological studies with clinical or neuropathological features. The development of non-isotopic molecular cytogenetic in situ hybridization (ISH) techniques which can be applied to archival tumour material provides an opportunity to address a wide range of neuropathological questions at a genetic level. Identification of specific chromosomes has been made possible by the isolation of probes which recognize the highly repeated sequences present in the centromeric regions of individual chromosomes. Libraries of human chromosome-specific painting probes are also available. A range of probes which bind to the whole or part of specific single copy genes are becoming available. These can be detected with either fluorochromes with different emission colours or with enzymatic detection systems in either interphase nuclei derived from fresh, fixed and embedded tumour samples, touch preparations or smears (so-called 'interphase cytogenetics') as well as conventional metaphase spreads. Comparative genomic hybridization can be used to scan the entire genome for deletions or amplifications without any pre-existing information about the likely locations of these abnormalities or the availability of any specific DNA probes. These techniques can be used to identify aneuploidy or structural alterations in individual chromosomes and are likely to yield important information about the location of genes important in the pathogenesis of brain tumours and may also provide the basis for the refinement of diagnostic or prognostic criteria of these neoplasms.