Apart from ERα and PR, numerous nuclear receptors, including the androgen receptor (AR), the vitamin D3 receptor (VDR), the retinoid X receptors (RXR), and the farnesoid X receptor (FXR) have been investigated as potential novel targets for the treatment of breast cancer because of their role as key regulators of gene expression [9,10,11,12]. The gene discussed is ESR1; the disease is breast cancer.