GPER1 and breast cancer: Studies revealed that activation of GPR30 can induce the expression of genes and activate pathways that facilitate cell proliferation of endometrial,11,12 breast,13 and ovarian cancer.14 On the contrary, numerous studies demonstrated that activation of GPR30 by its specific agonist G-1 results in cell-cycle arrest and proliferation inhibition of ERα-positive breast cancer,10 endothelial cells,15 prostate,16 and ovarian9 cancer cells.