To determine the effects of specific carotenoids on human breast cancer cells, we initially investigated the anti-proliferative effect of three carotenoids (lutein, β-carotene, astaxanthin) on the growth of human breast cancer cell lines (MCF-7 [ER/PR+HER2−] and MDA-MB-468 [triple-negative]), and normal primary human mammary epithelial cells (PmECs). The gene discussed is ESR1; the disease is breast carcinoma.