Estrogen-receptor (ER) negative breast cancer comprises 25–30% of all sporadic breast cancer and is characterized by advanced histological grade, aggressive clinical behavior, a high rate of metastasis to the brain and lung, and resistance to hormone deprivation therapy (Yersal and Barutca, 2014, Sorlie et al., 2001, Rakha et al., 2008a). This evidence concerns the gene ESR1 and breast cancer.