Advances in our understanding of the biology of paediatric central nervous 
system (CNS) tumours have encouraged pathologists to use molecular markers 
alongside histopathological analysis for disease classification or 
prognostication and treatment stratification. In this article, we review 
molecular genetic alterations in paediatric CNS tumours, including those in 
low-grade and high-grade gliomas, ependymomas, and embryonal tumours. Some of 
these molecular changes with clinicopathological utility have been used for the 
first time in the most recent edition of the World Health Organization (WHO) 
classification of CNS tumours to define entities like ependymoma, RELA 
fusion-positive or diffuse midline glioma, H3 K27M-mutant. The classification of 
paediatric CNS tumours is entering a new era when histopathologists must work 
with molecular genetic data and their molecular pathology colleagues to provide 
an optimal diagnostic evaluation for their patients and clinical colleagues. 
Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by 
John Wiley & Sons, Ltd.