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Anaplastic oligodendrogliomas have long attracted interest because of their sensitivity to chemotherapy, in particular in the subset of 1p/19q co-deleted tumors. Recent molecular studies have shown that all 1p/19q co-deleted tumors have IDH mutations and most of them also have TERT mutations. Because of the presence of similar typical genetic alterations in astrocytoma and glioblastoma, the current trend is to diagnose these tumors on the basis of their molecular profile. Further long-term follow-up analysis of both EORTC and RTOG randomized studies on (neo)adjuvant procarbazine, lomustine, vincristine (PCV) chemotherapy have shown that adjuvant chemotherapy indeed improves outcome, and this is now standard of care. It is also equally clear that benefit to PCV chemotherapy is not limited to the 1p/19q co-deleted cases; potential other predictive factors are IDH mutations and MGMT promoter methylation. Moreover, a recent RTOG study on low-grade glioma also noted an improved outcome after adjuvant PCV chemotherapy, thus making (PCV) chemotherapy now standard of care for all 1p/19q co-deleted tumors regardless of grade. It remains unclear whether temozolomide provides the same survival benefit, as no data from well-designed clinical trials on adjuvant temozolomide in this tumor type are available. Another question that remains is whether one can safely leave out radiotherapy as part of initial treatment to avoid cognitive side-effects of radiotherapy. The current data suggest that delaying radiotherapy and treatment with chemotherapy only may be detrimental for overall survival., (© 2016 Elsevier B.V. All rights reserved.)

Recent studies have shown that the clinical outcome of anaplastic oligodendroglial tumors is variable, but also that the histological diagnosis is subject to interobserver variation. We investigated whether the assessment of 1p/19q codeletion, polysomy of chromosome 7, epidermal growth factor receptor (EGFR) gene amplification (EGFR(amp)), and loss of chromosome 10 or 10q offers additional prognostic information to the histological diagnosis and would allow molecular subtyping. For this study, we used the clinical data and tumor samples of the patients included in multicenter prospective phase III European Organisation for Research and Treatment of Cancer (EORTC) study 26951 on the effects of adjuvant procarbazine, chloroethyl cyclohexylnitrosourea (lomustine), and vincristine chemotherapy in anaplastic oligodendroglial tumors. Fluorescence in situ hybridization was used to assess copy number aberrations of chromosome 1p, 19q, 7, 10, and 10q and EGFR. Three different analyses were performed: on all included patients based on local pathology diagnosis, on the patients with confirmed anaplastic oligodendroglial tumors on central pathology review, and on this latter group but after excluding anaplastic oligoastrocytoma (AOA) with necrosis. As a reference set for glioblastoma multiforme (GBM), patients from the prospective randomized phase III study on GBM (EORTC 26981) were used as a benchmark. In 257 of 368 patients, central pathology review confirmed the presence of an anaplastic oligodendroglial tumor. Tumors with combined 1p and 19q loss (1p(loss)19q(loss)) were histopathologically diagnosed as anaplastic oligodendroglioma, were more frequently located in the frontal lobe, and had a better outcome. Anaplastic oligodendroglial tumors with EGFR(amp) were more frequently AOA, were more often localized outside the frontal lobe, and had a survival similar to that for GBM. Survival of patients with AOA harboring necrosis was in a similar range as for GBM, while patients with AOA with only endothelial proliferation had better overall survival. In univariate analyses, all molecular factors except loss of 10q were of prognostic significance, but on multivariate analysis a histopathological diagnosis of AOA, necrosis, and 1p(loss)19q(loss) remained independent prognostic factors. AOA tumors with necrosis are to be considered WHO grade IV tumors (GBM). Of all molecular markers analyzed in this study, especially loss of 1p/19q carried prognostic significance, while the others contributed little prognostic value to classical histology.