Pathology and Molecular Biology

Classification of central nervous system (CNS) tumors during the last 10 years has improved thanks to molecular pathology that has enhanced our understanding of CNS tumors, providing new elements to integrate diagnosis. Multiple newly recognized pediatric-type diffuse low-grade and high-grade gliomas are defined in the new WHO classification, ependymoma and embryonal tumors. For some of these tumor types, the potential efficacy of small molecular inhibitors or other targeted therapies may affect future prognostication. This chapter focuses on general updates in the 2021 edition of the CNS WHO classification, with a particular focus on the histopathologic features of the newly recognized pediatric-type low-grade and high-grade tumor types. Nevertheless, the advance in genetic and epigenetic classification of pediatric CNS tumors, histopathology, and immunohistochemistry remain fundamental methodologies for CNS tumor classification and importantly guide practical further molecular testing.