Oligodendroglioma and oligoastrocytoma

Robert Grant MD (Dr. Grant of the Edinburgh Centre for Neuro-Oncology has no relevant financial relationships to disclose.)
Edward J Dropcho MD, editor. (Dr. Dropcho of Indiana University Medical Center has no relevant financial relationships to disclose.)
Originally released February 15, 1996; last updated September 27, 2015; expires September 27, 2018

This article includes discussion of oligodendroglioma and oligoastrocytoma, oligodendroglioma, anaplastic oligodendroglioma, oligoastrocytoma, and anaplastic oligoastrocytoma. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

The author reviews the evolving genotype and enzymatic research in oligodendroglioma and the associated clinical and imaging correlates in these radio- and chemo-responsive tumors. Molecular markers such as Ch1p19q, IDH1, MGMT-STP27, ATRX, and TP53 help more accurately classify oligoastrocytomas. Several studies have shown that molecular classification, especially 1p19q codeletion, corresponds with outcome better than histopathology. When surgery is required, maximum tumor resection should be performed where possible. When further treatment is required for progression in low-grade glioma, radiotherapy plus adjuvant procarbazine, lomustine, and vincristine (PCV) chemotherapy is superior to radiotherapy alone. Radiotherapy and adjuvant PCV chemotherapy is standard-of-care in patients with codeleted anaplastic oligodendroglioma. Radiotherapy alone after surgery in non-codeleted anaplastic oligodendrogliomas remains the treatment of choice at present, but patients with IDH1 mutations will respond better to chemotherapy than those without mutations. There remains debate, but no strong evidence, about whether temozolomide could be substituted for PCV, with similar effect and fewer toxicities.

Key points

 

• Oligodendrogliomas are slow-growing, and most present with epilepsy alone.

 

• The value of early intervention with radiotherapy or chemotherapy may be counterbalanced by late effects of treatment in low-grade oligodendroglioma.

 

• It is increasingly likely the term oligoastrocytoma will become redundant and molecular analysis will be used to diagnose either oligodendroglioma or astrocytoma with specific molecular signatures.

 

• Radiation and adjuvant procarbazine, lomustine, and vincristine (PCV) chemotherapy improves overall survival in patients with oligodendroglioma and anaplastic oligodendroglioma with codeletion at Ch 1p19q, compared to radiation alone.

 

• Chemotherapy does not improve survival in "non-deleted" patients with anaplastic oligodendroglioma.

 

• Quality of life with treatment is generally very good until the last year of life.

Historical note and terminology

Oligodendrogliomas were first reported by Bailey and Cushing in 1926 (Bailey and Cushing 1926). The World Health Organization divides oligodendrogliomas into 2 types: ("benign") oligodendroglioma and anaplastic ("malignant") oligodendroglioma. However, discriminating criteria are not well defined (Kleihues et al 1994). Oligodendroglioma requires the presence of mitoses (5 to 10 per high-power field [magnification x400]), "moderate" nuclear polymorphism, and "minimal" vascular endothelial proliferation. Anaplastic oligodendroglioma should be diagnosed when there are higher degrees of mitoses, nuclear polymorphism, and vascular endothelial proliferation or the presence of necrosis. Oligodendrogliomas can be "pure" or "mixed." "Pure" oligodendroglioma has been defined as where over 80% of cells are oligodendroglial. If over 20% of cells are astrocytic, tumors are called mixed oligoastrocytomas. The World Health Organization classification acknowledges mixed gliomas by classifying them separately as (a) mixed oligoastrocytoma, (b) anaplastic (malignant) oligoastrocytoma, and (c) others. Histological classification and typing of oligodendroglial tumors can be difficult with relatively low interobserver agreement, even between experienced neuropathologists (Aldape et al 2007; Hyder et al 2007). Most pure oligodendrogliomas have Ch1p and 19q deletions. Genotyping can confirm the accuracy of the histological diagnosis in this group. It has been found that loss of 1p centromere marker D1S2696 within the NOTCH2 intron 12 is associated with good prognosis in oligodendroglioma, and assessment of the intrachromosomal ratio between loss of 1p centromere marker D1S2696, within the NOTCH2 intron 12, and its 1q21 pericentric duplication N2N (N2/N2N test) distinguished oligodendrogliomas from glioblastoma with a specificity of 100% and a sensitivity of 97% (Boulay et al 2007). This could be a molecular test to detect prognostically favorable gliomas.

In 2007, the WHO introduced "glioblastoma multiforme with oligodendroglioma component" for necrotic anaplastic oligoastrocytomas. This may lead to an increase in glioblastomas of up to 10%, and as these tumors may have a better survival than primary glioblastomas. As a result, there may be an apparent improvement in survival of both glioblastomas and anaplastic oligodendrogliomas simply due to re-classification artefact (Wang et al 2012). Not all groups find that an oligodendroglial component is associated with a better prognosis (Hegi et al 2012).

In 2014, the International Society for Neuropathology-Haarlem consensus guidelines supported a 4-layered format for integrating morphological and molecular diagnosis of CNS tumor (Louis et al 2014). Layer 1 is the integrated diagnosis based on levels 1 to 4; layer 2 is the histological classification; layer 3 is the WHO grade; and layer 4 is the molecular information and how this was identified (eg, IDH1-R132H+ (IHC), Ip/19q deletion (FISH)).

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