ESR1 and breast cancer: Given the recent findings suggesting abiraterone can induce growth in ER+ breast cancer cells in vitro,23 we assessed the impact of abiraterone on the proliferation of a panel of cell lines modelling both oestrogen-dependent and independent growth (Fig. 1).31 Wt cell lines were grown in the absence of E2 for 5 days prior to the treatment with escalating concentrations of abiraterone.