ERα mainly has a stimulatory effect on cell proliferation and has been shown to be a tumor promoter in, for example, breast cancer, whereas ERβ mainly acts in the opposite way by exerting anti-proliferative and pro-apoptotic effects on multiple healthy [18–22] and tumor cell types, such as in breast [23], prostate [24] and ovarian cancer [25]. The gene discussed is ESR1; the disease is neoplasm.