Due to a lack of expression of the estrogen receptor or progesterone receptor, low mRNA levels of human prolactin receptor (hPRLR), or overexpression of human epidermal growth factor receptor (HER2) [33], it was surprising that human breast cancer cells gave rise to luminal cell progeny capable of producing milk proteins in this study [34]–[35]. The gene discussed is ESR1; the disease is breast cancer.