Molecular analysis is mandatory to define tumors with compatible features as “diffuse astrocytoma, MYB- or MYBL1-altered.” FISH may be useful to demonstrate rearrangements of MYB or MYBL1 genes, but sequencing allows to determine the nature of the fusion between MYB or MYBL1 and a partner gene (most frequently PCDHGA1, MMP16, and MAML2). The gene discussed is MYBL1; the disease is diffuse astrocytoma.