GPER1 and breast cancer: Given that prior work in breast cancer cell lines and fish oocytes determined that estrogen binding to GPER modulates cAMP (Filardo et al., 2002; Thomas et al., 2005; Cabas et al., 2013; Majumder et al., 2015; Pang and Thomas, 2010), and that cAMP signaling stimulates melanin synthesis, we thought it possible that GPER may be the physiologically relevant human melanocyte estrogen receptor.