To further validate our observations in the ATF2 dependency of tamoxifen-resistant breast cancer cells, ATF2 knockdown was performed in the independently derived endocrine-resistant MCF7 cells, LCC2 and LCC9 [29, 30] (Supplementary Fig. 2a–f) and showed similar results to the TAMR cells; ATF2 silencing significantly inhibited the growth of both LCC2 and LCC9 cell lines. This evidence concerns the gene ATF2 and breast cancer.