We selected three ER+ breast cancer cell lines (CAMA-1, MCF-7, and T47D) with above-average endocrine resistance, based on proliferation-corrected endocrine sensitivity estimates from a published large-scale drug screen (Hafner et al, 2017) (Data ref: Hafner 2017) (Appendix Fig. S1). This evidence concerns the gene ESR1 and breast carcinoma.