We validated these results in an independent cohort of 401 breast cancers with known ER status that we profiled DNA methylation using the HumanMethylation450K (HM450K) BeadChip array33 and found that ER+ tumours have lower levels of DNA methylation at ESR1 enhancers (Supplementary Fig. 4C). Here, ESR1 is linked to breast carcinoma.