Abstract.Background: Glioblastomas are the most common and most malignant brain tumors in adults. A small subgroup of glioblastomas contains areas with histological features of oligodendroglial differentiation (GBMO). Our objective was to genetically characterize the oligodendroglial and the astrocytic parts of GBMOs and correlate morphologic and genetic features with clinical data.Methods: The oligodendroglial and the "classic" glioblastoma parts of 13 GBMO were analyzed separately by interphase fluorescence in situ hybridization (FISH) on paraffin sections using a custom probe set (regions 1p, 1q, 7q, 10q, 17p, 19q, cen18, 21q) and by comparative genomic hybridization (CGH) of microdissected paraffin embedded tumor tissue.Results: We identified four distinct genetic subtypes in 13 GBMOs: an "astrocytic" subtype (9/13) characterized by +7/−10; an "oligodendroglial" subtype with −1p/−19q (1/13); an "intermediate" subtype showing +7/−1p (1/13), and an "other" subtype having none of the former aberrations typical for gliomas (2/13). The different histological tumor parts of GBMO revealed common genetic changes in all tumors and showed additional aberrations specific for each part.Conclusion: Our findings demonstrate the monoclonal origin of GBMO followed by the development of the astrocytic and oligodendroglial components. The diagnostic determination of the genetic signatures may allow for a better prognostication of the patients.

Our findings demonstrate the monoclonal origin of GBMO followed by the development of the astrocytic and oligodendroglial components. The diagnostic determination of the genetic signatures may allow for a better prognostication of the patients.

In contrast to astrocytic tumors including glioblastomas (GBM), oligodendrogliomas (O) show a better prognosis and increased responsiveness to chemotherapy. Interestingly, a small subgroup of glioblastomas contains areas with histological features of oligodendroglial differentiation. In the current WHO classification (2007) these tumors are now included as a variant of glioblastomas and are called glioblastomas with oligodendroglial component (GBMO). However, definitive diagnostic criteria still do not exist. In this study we used a genome wide approach (chromosomal comparative genomic hybridization (CGH) and molecular karyotyping) in combination with interphase fluoreszence in situ hybridization (FISH) (regions 1p, 1q, 7q, 10q, 17p, 19q, cen18, 21q) to genetically characterize GBMO and “classical” O. We analyzed the oligodendroglial and the astrocytic glioblastoma parts of 13 GBMO separately by chromosomal CGH of microdissected paraffin embedded tumor tissue and interphase FISH on paraffin sections. Furthermore, freshly frozen material of six oligodendrogliomas (4 WHO grade II, 6 WHO-grade III) was examined genome wide by using the standard Agilent 244A chip. We identified four distinct genetic subtypes in GBMO: an “astrocytic” subtype (9/13) characterized by +7/-10; an “oligodendroglial” subtype with −1p/-19q (1/13); an “intermediate” subtype showing +7/-1p (1/13), and an “other” subtype having none of the former aberrations typical for gliomas (2/13). In contrast, most “classical” O (5/6) showed combined 1p/19q deletion, corresponding genetically to the “oligodendroglial” subtype. Four of the O with 1p/19q codeletion showed additional aberrations (e. g. −4, −14, −9, −18). The different histological tumor parts of GBMO revealed common genetic changes in all tumors and showed additional aberrations specific for their oligodendroglial and astrocytic parts. These findings demonstrate the monoclonal origin of the tumor followed by the formation of the astrocytic and oligodendroglial components. We are currently evaluating the array CGH results of six oligodendrogliomas, which will also be presented. The diagnostic determination of these genetic signatures may allow for a better prognostication of the patients. Our results underline the importance of molecular cytogenetic analyses to supplement the histological diagnosis of gliomas. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 782.