The effect of WHO reclassification of necrotic anaplastic oligoastrocytomas on incidence and survival in glioblastoma

Abstract

In 2007 the WHO Classification of Tumours of the Central Nervous System introduced the entity “glioblastoma with oligodendroglioma component” (GBM/OLIGO). This entity accounts for approximately one in every ten new glioblastomas (GBM). In practice, those mixed gliomas with necrosis which were previously diagnosed as anaplastic oligoastrocytoma (AOA) are now designated glioblastoma with oligodendroglioma component. In this way we diagnose as glioblastomas some tumours we already know for which survival is longer than for “classic” glioblastomas. Oncologists should be aware that some newly diagnosed cases of GBM, specifically those called GBM/OLIGO, may behave as AOA. In the next few years we could observe two consequences of this: first, if anaplastic oligoastrocytomas with necrosis are now to be diagnosed as glioblastomas with oligodendroglioma component, obviously it must be expected that the incidence of glioblastoma will increase in these years; second, because these tumours with known longer median OS are now included in the group of glioblastomas, improvement in the survival of patients with glioblastoma in the next few years should be ascribed not only to advances in diagnosis and treatment but also to a semantic factor.