**Oligoastrocytoma: A Vanishing Tumor Entity**

Marta Mellai, Laura Annovazzi, Marta Mazzucco and Davide Schiffer

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/63240

#### **Abstract**

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338 Neurooncology - Newer Developments

Oligoastrocytoma (OA) was a glioma recognized in the current World Health Organization (WHO) classification of the central nervous system (CNS) tumors as a mixed tumor with an astrocytic and an oligodendroglial component. Its definability was, however, poor so that its prevalence varies in the various collections. A series of contributions of the literature and the "International Society of Neuropathology (ISN) – Haarlem *Consensus*" recently denied its existence as a tumor entity on the basis of 1p/19q, isocitrate dehydrogenase (IDH) and α-thalassemia/mental retardation syndrome X-linked (ATRX) status. Most tumors previously diagnosed as OAs were, therefore, reclassified as either oligodendro‐ gliomas or astrocytomas.

We revised 40 OAs from our glioma series initially diagnosed with stringent histologic criteria. After the revision based on the above mentioned molecular markers, most of them changed diagnosis falling into the categories of oligodendroglioma or astrocytoma. Only one fulfilled the stringent criteria of the current classification system, whereas two cases remained undefined.

Since ATRX is constitutively expressed in microglia/macrophages, their number in the histologic sections has a paramount importance in recognizing the oligodendroglial component. The double ATRX/GFAP, ATRX/IDH1R132H and ATRX/Iba-1 immunostain‐ ings greatly conditions the recognition of the oligodendroglial and astrocytic tumor cells.

**Keywords:** oligoastrocytoma, 1p/19q co-deletion, IDH, ATRX, prognosis

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
