ESR1 and breast cancer: The first membrane-associated ER that was identified was GPR30.It was demonstrated that the translocation of GPR30 to the cell surface significantlyincreased after estrogen treatment in tamoxifen-resistant breast cancer cells and itsactivity was mediated through the EGFR (Ignatovet al. 2010, Mo etal. 2013) and it is able to attenuate the inhibition of MAPK as well(Mo et al. 2013).