The G protein‐coupled estrogen receptor (GPER, nomenclature as agreed by the NC‐IUPHAR Subcommittee on the G protein‐coupled estrogen receptor [1607]) was identified following observations of estrogen‐evoked cyclic AMP signalling in breast cancer cells [65], which mirrored the differential expression of an orphan 7‐transmembrane receptor GPR30 [276]. This evidence concerns the gene GPER1 and breast cancer.