Although a general limitation of this study is the use of a transformed human breast cancer cell line, which displays differences from normal MECs with regard to the abundance of certain receptors, such as estrogen receptors [55], and the response to non-physiological (e.g. exogenous retinoic acid) stimuli [56], both MCF-7 cells and normal MECs cells exhibit a similar regulation by important lactogenic hormones including oxytocin and prolactin [57–59]. This evidence concerns the gene ESR1 and breast cancer.