This large group of tumours is highly heterogeneous, causing major diagnostic challenges, and also encompasses newly recognised types in the fifth edition of the World Health Organisation (WHO) CNS tumours, such as diffuse astrocytoma, MYB/MYBL1 altered, polymorphous low‐grade neuro‐epithelial tumour of the young and diffuse low‐grade, MAPK pathway‐altered. The gene discussed is MYBL1; the disease is diffuse astrocytoma.