Although single base-pair resolution DNA methylation landscapes for embryonic and different somatic cell types provided important insights into epigenetic dynamics and cell-type specificity, such comprehensive profiling is incomplete across human cancer types. This prompted us to perform genome-wide DNA methylation profiling of 22 samples derived from normal tissues and associated neoplasms, including primary tumors and cancer cell lines. Unlike their invariant normal counterparts, cancer samples exhibited highly variable CpG methylation levels in a large proportion of the genome, involving progressive changes during tumor evolution. The whole-genome sequencing results from selected samples were replicated in a large cohort of 1112 primary tumors of various cancer types using genome-scale DNA methylation analysis. Specifically, we determined DNA hypermethylation of promoters and enhancers regulating tumor-suppressor genes, with potential cancer-driving effects. DNA hypermethylation events showed evidence of positive selection, mutual exclusivity and tissue specificity, suggesting their active participation in neoplastic transformation. Our data highlight the extensive changes in DNA methylation that occur in cancer onset, progression and dissemination.

This work was supported by Institute of Health Carlos III ISCIII Project no. PI11/00321, Spanish Cancer Research Network (RTICC) no. RD12/0036/0039; European Development Regional Fund, ‘A way to achieve Europe’ ERDF (SAF2014-55000-R), Sandra Ibarra Foundation; Olga Torres Foundation; Cellex Foundation; AGAUR 2014SGR633 grant; Health and Science Departments of the Catalan government (Generalitat de Catalunya) and European Community's Seventh Framework Program (FP7/2007-2013), grant HEALTH-F5-2011-282510 – BLUEPRINT. HH is a Miguel Servet (CP14/00229) ISCII researcher.