Glioblastomas with an oligodendroglial component: A pathological and molecular study

Glioblastoma (GBM) is considered by the WHO classification to represent the most malignant grade of the astrocytic tumors. However, a subset of GBIVI includes recognizable areas with oligodendroglial features, suggesting that some GBM may also have an oligodendroglial origin. The aim of this study was to analyze the molecular profile of GBIVI associated with an oligodendroglial component (GBMO). We analyzed a series of 25 GBMO. Loss of heterozygosity (LOH) on I p and l9q, known as common markers of oligodendroglial tumors, were observed in 4017c and 60% of cases, respectively; 72% of the tumors displayed one or both of these markers. All but 4 tumors (84%) showed alterations known to be preferentially involved in the progression of astrocytic tumors to GBM, such as EGFR amplification (44%), P16 deletion (48%), LOH on 10q (64%). PTEN (20%), and TP53 (24%) mutations. Therefore, GBMO displayed all the genetic aberrations found in "standard" GBM with a comparable incidence, but differed from GBM by having a higher rate of LOH on lp and 19q. These results suggest that GBMO might represent a subgroup of tumors of oligodendroglial origin that is distinct from the "standard" GBM in terms of turnorigenesis pathway.