ESR2 and breast cancer: Gene Cluster C contained NRs whose activation has been associated with the inhibition of breast cancer cell growth, including GR, RARβ, RARγ, RORα, PPARγ and VDR [16, 17], as well as ERβ, TR2 and TR4 whose role in breast cancer may lie, at least in part, with their action in reducing or inhibiting ERα activity [31–33].