The set of breast tissue samples used previously [24] was analyzed for the methylation status of the following seven genes: adenomatous polyposis coli (APC); breast cancer 1, early onset (BRCA1); cyclin-dependent kinase inhibitor 2A (CDKN2A, p16); estrogen receptor α (ESR1); estrogen receptor β (ESR2); human epidermal growth factor receptor 2 (HER2/neu); and phosphatase and tensin homolog (PTEN). This evidence concerns the gene ESR1 and breast cancer.