Genistein regulated the proliferation and mitochondrial functionality of breast cancer cells in an ERα/ERβ ratio-dependent way, since genistein treatment induced cell cycle arrest and improved mitochondrial functionality in T47D cells (low ERα/ERβ ratio), without affecting MCF-7 (high ERα/ERβ ratio) and MDA-MB-231 (ER-negative) cells [58]. The gene discussed is ESR2; the disease is breast cancer.