The immunophenotype—diffuse GFAP and S100, strong nuclear SOX10, retained ATRX, and negative IDH1 R132H with tumor-cell negativity for CD31/CD34—supports a circumscribed astrocytic tumor and argues against IDH-mutant diffuse astrocytoma, ependymoma (typically SOX10-negative and often epithelial membrane antigen (EMA)-dot positive), and central neurocytoma/glioneuronal tumors (which would show neuronal marker expression) (16, 17). The gene discussed is PECAM1; the disease is diffuse astrocytoma.