Previous studies have established that the differential expression of ER and SRC proteins modulates estrogenic action during tumorigenesis of breast cancer: in a group of breast cancer specimens, the expression of ERα significantly correlated with that of PR and nuclear receptor corepressor 1 (NCoR1), whereas ERβ expression was associated with NCOA1 and NCOA2 expression (46). This evidence concerns the gene ESR1 and breast cancer.