It is nowadays well-established (Merenbakh-Lamin et al., 2013; Robinson et al., 2013; Toy et al., 2013; Jeselsohn et al., 2014) that distinct ERα polymorphisms (mERαs), located in the vicinity of LBC (i.e., E380Q), between H9 and H10, or in the loop connecting H11 and H12 (i.e., L536Q, L536R, Y537C, Y537N, Y537S, and D538G), are recurrently observed in metastatic BC patients relapsing after extended treatments regimens. Here, ESR1 is linked to breast cancer.