We observed the reduced accessibility of EREs in two independent cohorts (42 and 75 samples in the JFCR–BRCA and TCGA–BRCA cohorts, respectively), suggesting that the current classification system for ER-positive tumours based on gene expression, particularly the expression of ER, PgR and Ki67, is not sufficient for understanding the nature of BC. Here, MKI67 is linked to neoplasm.