Glioblastoma with oligodendroglioma component: A review of clinical, morphologic, and molecular characteristics

Glioblastoma (GBM), the most common primary brain tumor, has a dismal prognosis with an average survival of only 1 year following standard therapy. In 2007, the World Health Organization recognized a new subtype of GBM, the GBM with oligodendroglioma component (GBM-O). Glioblastomas with oligodendroglioma component have features of conventional GBMs with an infiltrative astrocytoma component, microvascular proliferation, and necrosis as well as a prominent oligodendroglioma component. The oligodendroglioma component should be morphologically classic and display round, monotonous cells with perinuclear halos. Since the description of GBM-O in 2007, several studies have assessed their clinical characteristics, morphology, molecular profiles, and outcomes. As a group, patients with GBM-O are younger than those with classic GBM, and age is one of the most important prognostic factors for GBM-Os, similar to classic GBMs. Other clinical factors impacting survival of patients with GBM-Os include treatment differences and whether the tumor is primary or secondary. Most studies indicate that 1p and 19q deletion and IDH1 mutations are more frequent in GBM-O than classic GBMs and have prognostic significance. Other genetic alterations, such as EGFR amplification, PTEN deletion and mutation, TP53 mutation, CDKN2a/p16 deletion, and MGMT promoter methylation, are present in GBM-Os with similar frequencies to classic GBM. Patients with GBM-O generally have a more favorable clinical outcome compared with those with classic GBM.