GFAP and glioblastoma: As in the presented case, glioblastoma with epithelial differentiation should have epithelial morphology and immunopositivity for epithelial markers, such as cytokeratins CAM2.5, AE1/3, 7, and 20.2 While cytokeratin AE1/3 antibodies can sometimes cross-react with GFAP, that did not occur in this case (compare Figure 2F with 2G).7 Such tumors also tend to have TP53 mutations and some sort of cell cycle-activating alteration, most commonly CDKN2A/B deletion.2 In the current case, that activation was in the form of CDK4 amplification.