The ER+ breast cancer cell lines T47D, MCF7, the ER- MDA-231, BT-474 and the non-tumorigenic epithelial cell line MCF10A were chosen for varying levels of PRLr expression (relative PRLr expression: T47D>MCF7>BT-474≈ MDA-231≈ MCF10A) [25,26]. Here, ESR1 is linked to breast cancer.