Our results that activation of GPR30 inhibited the proliferation of ER− breast cancer cell is convenient with the growth arrest effects of GPR30 activation reported in many cancer types such as prostate,16 Leydig,30 urothelial cell,31 ovarian,9 and ERα-positive breast cancer.10 In contrast, there were also studies showed that activation of GPR30 is able to stimulate cell growth of endometrial,11 ovarian,14 and breast cancer cells.32 It should be noted that the stimulatory effects of GPR30 are stimulated with non-specific agonists such as estrogen and tamoxifen. Here, GPER1 is linked to breast cancer.