Amongst patients presenting with ER positive primary tumors and for whom paired data for ER expression in the asynchronous metastases could be retrieved from the clinical records (N = 101), 17 (17%) lost ER expression at recurrence, which conveyed a significantly inferior breast cancer survival (Figure 1C, HR = 2.6, CI = 1.5–4.7, P = 0.002). Here, ESR1 is linked to breast cancer.