Glioblastoma with oligodendroglial component represents a subgroup of glioblastoma with high prevalence of IDH1 mutation and association with younger age

Glioblastoma with an oligodendroglial component (GBMO) is recognized as a subgroup of glioblastoma (GBM); however, the molecular and clinicopathological characteristics of GBMO are obscure. We evaluated the methylation status of MGMT, IDH1/2 mutation, deletions of 1p and 19q and expression of IDH1, p53, p16, CD151, and galectin3 proteins in 42 GBMOs (32 primary and 10 secondary tumors). Our aims were to correlate our molecular findings with clinicopathologic features, and to compare molecular-to-clinical correlations in the 42 GBMOs with the corresponding correlations in 45 GBMs. GBMO was subdivided into two subgroups according to the predominant cell component comprising > 50 % of tumors: the astrocytic predominant type (GBMO-A) and oligodendroglioma predominant type (GBMO-O). Methylation of MGMT, IDH1/2 mutation, and co-deletion of 1p and 19q were found in 31.0, 26.2, and 17.9 % of patients with GBMO, respectively. Clinicopathological and molecular characteristics did not differ significantly between GBMO-A and GBMO-O. However, patients with GBMO-O experienced better outcomes than patients with GBMO-A (p = 0.007). On multivariate analysis the predominant cell type was an independent prognostic factor in overall survival [hazard ratio 4.2 (95 % confidence interval 1.4-12.8), p = 0.011]. When compared to patients with classic GBM, those with GBMO were younger (49.21 vs. 57.47, p = 0.003) and more frequently had tumors with IDH1 mutation (23.8 vs. 4.4 %, p = 0.009). Survival was similar in patients with GBMO and with classic GBM. Based on these results, GBMO may represent a subgroup of GBM that is associated with IDH1 mutation and younger age, although similar to classic GBM in prognosis.