The clinical impact of these changes in receptor was reflected by the physicians who accrued patients to this study and who considered that the information from ER, PR, and HER2 assessment of the locoregional recurrence or metastatic disease would change the therapies offered in 17% of patients, emphasizing the potential of biopsy of breast cancer recurrence to positively influence therapeutic decision making [3,4,16,17]. Here, ESR1 is linked to breast cancer.