Accumulating γH2AX foci were also induced by IGF-1R depletion in MCF7 cells (Fig. 1C), and by xentuzumab treatment in a second ER+ breast cancer cell line, ZR-75-1 (Supplementary Fig. S1A), consistent with our previous findings in prostate and breast cancer cells [10, 14]. Here, IGF1R is linked to breast cancer.