A mastectomy, along with a right axillary lymph node dissection, were performed and the tumor was classified as stage PT3N2M0(IIIA) according to the TNM Staging System for Breast Cancer adopted by the American Joint Committee on Cancer (AJCC), (luminal B, estrogen receptor [ER] positive, progesterone receptor [PR] positive and human epidermal growth factor [HER] 2 positive). This evidence concerns the gene ESR1 and breast cancer.