GFAP and glioma: The tumor at this stage was not easily distinguishable from nontumor tissues without YFP immunohistochemistry, yet both PDGFRα, an oligodendrocyte precursor cell (OPC) marker, and GFAP, an astrocyte marker, were ectopically expressed on the tumor side, indicating that the tumor is a glioma (Figure 3i–l).