(13) were the first to describe a competitive binding (Ki values in the 10-7 M range) between estrogen and tamoxifen for GPER-1 expressed by SKBr3 breast cancer cells (ERα and ERβ negative, GPER-1 positive) or expressed by HEK cells transfected with GPER-1. The gene discussed is ESR2; the disease is breast carcinoma.