Subtyping of oligo-astrocytic tumours by comparative genomic hybridization

Oligo-astrocytic tumours (OAs) histologically show both oligodendroglial and astrocytic differentiation. Unequivocal criteria for delineation of OAs from pure oligodendroglial (Os) and astrocytic (As) tumours and for grading of OAs are lacking. Molecular genetic analysis may allow for a better characterization of OAs and thereby guide prognostic and therapeutic decisions. Comparative genomic hybridization (CGH) was performed on 39 gliomas with variable phenotypic expression of histological features characteristic of both astrocytic and oligodendroglial differentiation. The results show that OAs are genetically more heterogeneous than Os. In addition to the '-1p/-19q' and '+7/-10' subtypes that have been previously recognized, two additional genetic subtypes, 'intermediate' and 'other', were identified in the present study. 'Intermediate' OAs likely represent progression from '-1p/-19q' tumours. The 'other' subtype appears to represent an additional, heretofore unrecognized, genetic pathway(s). Application of rigorously 'strict' histopathological criteria, as opposed to 'relaxed' criteria, for the selection of oligo-astrocytic tumours resulted in a higher percentage of '-1p/-19q' tumours, but some '-1p/-19q' tumours might be missed. The results suggest that molecular genetic analysis is a useful and valid additional tool for the classification of gliomas, particularly for the significant subset of tumours in which subjective histopathological criteria are insufficient for an unequivocal distinction between Os, As, and mixed OAs.