Updated project metadata. Wild type (wt) MCF7 cells, modelling breast cancer at primary diagnosis, were cultured in phenol red-free RPMI supplemented with 10% FBS and 1nM estradiol (E2). Long-term oestrogen deprived (LTED) cell lines, which model resistance to endocrine therapy, were cultured in phenol red-free RPMI in the absence of exogenous E2 and supplemented with 10% dextran charcoal-stripped bovine serum (DCC). Samples were harvested at baseline and at the point of resistance (LTED). In order to do comparative analysis in the ER-interactome of wt-MCF7 and MCF7-LTED cells, ER-RIME (rapid immunoprecipitation mass spectrometry of endogenous proteins) was conducted in these cells.