GPER1 and breast cancer: The G‐protein‐coupled estrogen receptor GPR30 (also referred to as GPER or GPER1) was first reported by Carmeci et al17 using differential cDNA library screening from a breast cancer cell line; it was subsequently demonstrated to be the membrane estrogen receptor that mediates nongenomic estrogenic effects on target genes.18, 19 GPR30 immunoreactivities have been detected in the neuronal plasma membrane,20, 21 Golgi apparatus, and endoplasmic reticulum21, 22, 23 of female mice and/or rats.