The mechanism involved in the calcitriol-dependent ERα induction in ER-negative BC cells implicates the direct interaction of the VDR-RXR complex to VDREs in the ERα gene promoter region, including the inhibition of histone deacetylases (HDAC) and DNA methyltransferase (DNMT) enzymatic activity [166]. This evidence concerns the gene ESR1 and breast cancer.