However, the findings are consistent with the assumption that it may be worth testing the neoadjuvant application of a chemotherapy free approach to women with early breast cancer and HER2+ tumors while investigating in more detail the relative role and need for a pharmacologic block of the estrogen receptor, the cell cycle, the erbB-family of receptors and achieve an effective therapy tailored to the individual characteristics of the tumor. Here, ESR1 is linked to breast cancer.