Molecular characteristics of glioblastoma with 1p/19q co-deletion

Recent developments in molecular analysis have revealed genetic alterations in human gliomas. Loss of heterozygosity (LOH) is a critical molecular marker for classification of human glioma, and is useful for predicting outcome. Our previous LOH study identified a small subgroup of glioblastoma (GBM), with 1p/19q co-deletion, with a favorable clinical outcome. In this study, we investigated molecular pathological features of eight GBM with 1p/19q co-deletion compared with classic GBM and anaplastic oligodendroglioma (AO). We estimated EGFR gene amplification, EGFRvIII expression, CDKN2A (p16) homozygous deletion, and isocitrate dehydrogenase 1/2 (IDH1/2) gene mutations. We also conducted an analysis of the expression of proneural genes (DLL3, OLIG2, SOX2). On histopathological review, only one GBM was diagnosed as glioblastoma with oligodendroglioma component (GBMO). Loss of chromosomes 10 and 17p is common, and neither IDH1/2 mutations nor EGFRvIII expression were detected in GBM with 1p/19q co-deletion. The expression profile revealed high expression of the OLIG2 gene in this subgroup. High expression of proneural gene OLIG2 without EGFRvIII expression may be associated with a favorable clinical outcome; however, IDH1/2 gene status and the extent of LOH regions may indicate that this small subgroup of GBM is a distinct genetic subgroup from oligodendroglial tumors.