While previous studies have demonstrated that AR inhibitors can radiosensitise AR+ models of TNBC, prostate cancer and glioblastoma [7, 8, 16, 25, 27, 45, 46], in this study we demonstrate that pharmacologic inhibition, degradation, or genetic knockout of AR using CRISPR-Cas9, is not sufficient to radiosensitise AR+/ER+ breast cancer cell lines in vitro (Figs. 1, 2, 4, Supplementary Fig. 3). Here, ESR1 is linked to glioblastoma.