Characterization of gliomas: from morphology to molecules

This article reviews the histologic and molecular characterization of gliomas, including the new "integrated diagnoses" of the World Health Organization Classification, 2016 edition. The entities reviewed within include diffuse gliomas (astrocytoma, oligodendroglioma, glioblastoma), as well as circumscribed and low-grade gliomas (angiocentric glioma, pilocytic astrocytoma, subependymal giant cell astrocytoma, pleomorphic xanthoastrocytoma, pilomyxoid astrocytoma, ependymoma, myxopapillary ependymoma, and subependymoma). Diagnostic, prognostic, and predictive biomarkers are discussed for each entity. We review how molecular testing for IDH1 and ATRX and detection of chromosome 1p/19q codeletion can be used to categorize glioblastomas as IDH-wildtype or IDH-mutant, and lower grade diffuse gliomas into three molecular groups that correlate better with patient outcomes than histologic subtyping. Pediatric diffuse gliomas are highlighted, including diffuse midline glioma, H3 K27M-mutant, and inherited germline mutations that predispose to pediatric gliomas. The utility of genomic profiling of certain gliomas is discussed, including identifying candidates for experimental therapies. This review is meant to be a concise summary of glioma characterization for the practicing pathologist.