ESR1 and breast neoplasm: Importantly, we found that ATAC-seq peaks in patient breast tumours that are occupied by both ER and MAF in MCF7 cells are functionally connected to control of the E2 target gene expression through promoter–enhancer connections, to a higher degree than expected by chance (for example, SOX9 versus an approximate random permutation, P < 0.0001; Fig. 6c,d).