As examples, the DNA methylation class ‘infantile hemispheric glioma’ exclusively comprised hemispheric tumors in infants with frequent focal amplifications on cytoband 2p23.2, indicative of fusions involving the ALK gene9,10; the DNA methylation class ‘PXA’ comprised hemispheric tumors across ages consistently harboring homozygous deletions of the CDKN2A/B locus (9p21.3); and the DNA methylation class ‘ETMR’ comprised predominantly occipital or posterior fossa tumors in young children with a pathognomonic amplification at 19q13.42 (ref. 11). Here, CDKN2A is linked to central nervous system cancer.