Glioblastomas: correlation between oligodendroglial components, genetic abnormalities, and prognosis.

It has been demonstrated that a small percentage (approximately 15%) of glioblastomas (GBM) presents an oligodendroglial component with a variable frequency of chromosome 1p and 19q deletions, the genetic alteration related to chemotherapy response and longer survival in oligodendrogliomas. There is a growing interest in investigating 1p and 19q losses in hybrid gliomas and their impact on prognosis. A series of 88 GBMs was investigated regarding 1p and/or 19q losses, 24 with oligodendroglioma-like areas, using quantitative microsatellite analysis and/or fluorescent in situ hybridization. When present, the oligodendroglial and astrocytic components were independently investigated. Clinical data, histology, and 1p/19q status were correlated. Tumors with oligodendroglial components showed three cases each of 1p or 19q loss and one with combined 1p/19q loss. No difference in 1p or 19q status was observed between the oligodendroglial and astrocytic components. Conventional GBM demonstrated isolated 1p loss in four cases and 19q loss in five. No association was seen between 1p/19q status and histology. Deletions at 1p and/or 19q were infrequent in GBMs with oligodendroglial components. Despite the hybrid phenotype, the pattern of genetic changes at 1p and 19q was not different from that usually observed in conventional GBMs, nor did it show any correlation with survival.