Original contribution Nogo-A: a useful marker for the diagnosis of oligodendroglioma and for identifying 1p19q codeletion ☆ Gianluca Marucci MD ⁎ , Enrico Di Oto BSc, Anna Farnedi BSc, PhD, Riccardo Panzacchi MD, Claudia Ligorio BSc, Maria P. Foschini MD Section of Pathology “M. Malpighi,” Department of Haematology and Oncological Sciences «L. and A. Seragnoli», Bellaria Hospital, University of Bologna, 40139 Bologna, Italy Received 29 January 2011; revised 28 April 2011; accepted 4 May 2011 Keywords: Nogo-A; Olig-2; Oligodendroglioma; 1p/19q; FISH Summary The differential diagnosis between oligodendrogliomas and other gliomas remains a critical issue. The aim of this study is to verify the diagnostic value of Olig-2, Nogo-A, and synaptophysin and their role in identifying 1p19q codeletion. A total of 168 cases of brain tumors were studied: 24 oligodendrogliomas, 23 anaplastic oligodendrogliomas, 2 oligoastrocytomas, 2 anaplastic oligoastrocy- tomas, 30 glioblastoma multiforme, 2 diffuse astrocytomas, 4 anaplastic astrocytomas, 10 pilocytic astrocytomas, 9 ependymomas, 12 anaplastic ependymomas, 10 central neurocytomas, 10 meningiomas, 10 choroid plexus papillomas, 10 dysembryoplastic neuroepithelial tumors, and 10 metastases. All cases were immunostained with Olig-2, Nogo-A, and synaptophysin. In 79 cases, the status of 1p/19q had already been assessed by fluorescence in situ hybridization. Thus, in selected cases, fluorescence in situ hybridization was repeated in areas with numerous Nogo-A–positive neoplastic cells. Nogo-A was positive in 18 (75%) of 24 oligodendrogliomas, 8 (80%) of 10 dysembryoplastic neuroepithelial tumors, 6 (20%) of 30 glioblastoma multiforme, and 2 (20%) of 10 pilocytic astrocytomas. Olig-2 stained 22 (91.6%) of 24 oligodendrogliomas and all dysembryoplastic neuroepithelial tumors but also 24 (80%) of 30 glioblastoma multiforme and 8 (80%) of 10 pilocytic astrocytomas. Finally, synaptophysin stained 13 (54.1%) of 24 oligodendrogliomas, 3 (10%) of 30 glioblastoma multiforme, 1 (10%) of 10 pilocytic astrocytomas, and all neurocytomas. Among the 79 tested cases, original fluorescence in situ hybridization showed 1p/19q codeletion in 12 (52.2%) of 23 oligodendrogliomas, 8 (38%) of 21 anaplastic oligodendrogliomas, and 1 (4%) of 25 glioblastoma multiforme. However, after carrying out the Nogo-A–driven fluorescence in situ hybridization, 1p/19q codeletion was observed in 8 additional cases. Nogo-A is more useful and specific than Olig-2 in differentiating oligodendrogliomas from other gliomas. Furthermore, using a Nogo-A–driven fluorescence in situ hybridization analysis, it is possible to identify a larger number of 1p19q codeletions in gliomas. © 2012 Elsevier Inc. All rights reserved. ☆ Conflict of interest statement: The authors declare that they have no conflict of interest. ⁎ Corresponding author. Section of Pathology, Bellaria Hospital, University of Bologna, 40139 Bologna, Italy. E-mail address: gianluca.marucci@ausl.bologna.it (G. Marucci). www.elsevier.com/locate/humpath 0046-8177/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.humpath.2011.05.007 Human Pathology (2012) 43, 374–380