Coexpression of glial and neuronal markers in the neurocytic rosettes of rosette-forming glioneuronal tumors.

Rosette-forming glioneuronal tumor of the fourth ventricle (RGNT) is a new entity in the WHO 2007 Classification of Tumors of the Central Nervous System. RGNT has two components: neurocytic rosettes and low-grade gliomas. Neurocytic rosettes are conventionally described as consisting of uniform neurocytes. However, some studies have reported rosette-forming tumor cells that expressed glial markers such as Olig2. We indicated the expression of glial markers including Olig2, cyclinD1, glial fibrillary acidic protein (GFAP), and platelet-derived growth factor receptor alpha (PDGFRα) in the neurocytic rosettes in our previous study, and we suggested that these tumor cells had a heterogeneous nature. In this study, we used double and triple immunostaining to demonstrate that these tumor cells have both glial and neuronal characteristics. We found that rosette-forming tumor cells coexpressed Olig2/cyclinD1 and synaptophysin. Furthermore, the cores of the rosettes coexpressed GFAP/PDGFRα in the peripheral zone and synaptophysin in the central zone. These findings imply that rosette-forming tumor cells have a similar nature to neuronal-glial progenitor cells, and we believe that the nomination "neurocytic rosette" may be unsuitable given their heterogeneous nature. Our study appears to clarify some of the properties of RGNT tumor cells and may help elucidate the histogenesis of RGNT.