ESR1 and breast cancer: Molecular subtyping of BC depending on estrogen, progesterone, and HER2 status to divide the disease into subtypes: luminal A (ER(+) and /or PR(+) Her2 (−)), luminal B (ER(+) and /or PR(+) Her2 (+)), triple negative(ER(−) and /or PR(−) Her2 (−)).