Analyses were adjusted for established prognostic factors in MBC including age, Eastern Cooperative Oncology group (ECOG) performance status, NHG, breast cancer subtype (ER+/HER2−, HER2+, TNBC), metastasis-free interval (MFI), number of metastatic sites (< 3 / >=3) and site of metastasis (visceral / non-visceral). Here, ESR1 is linked to breast cancer.