Considering that diverse environmental contaminants exhibit binding affinity for GPER (Thomas and Dong 2006), we performed ligand-binding studies using radiolabeled E2 as a tracer in ER-negative and GPER-positive SkBr2 breast cancer cells (Lappano et al. 2010, 2012a, 2012b). This evidence concerns the gene GPER1 and breast cancer.