The 9 breast cancer cell lines used in this study are representative of 4 subtypes determined based on their tumor origin, hormone receptor status (expression profile of estrogen receptor, progesterone receptor and HER2) and mutations: (1) luminal A-like (T-47D and ZR-75-1), (2) luminal B-like HER2+ (SK-BR-3), (3) HER2-enriched (HCC1569 and HCC1954) and (4) basal-like TN (MDA-MB-468, Hs-578T, BT-549 and MDA-MB-231) (Additional file 1: Table S1). Here, ESR1 is linked to breast cancer.