In physiological concentrations (1 nM corresponding to peak nighttime and 10 pM corresponding to day time serum values in humans), melatonin suppresses the growth of ER-positive (MCF-7, T47D, ZR 75-1) and some ER-negative (MDA-MB-468) human breast cancer cell lines in vitro[45]. This evidence concerns the gene ESR1 and breast cancer.