TP53BP1 and breast cancer: First, to determine the rate of DSB repair prior to radiation exposure, the number of 53BP1 foci per cell nucleus was counted in confocal images of mammary tissues from nonirradiated rats, indicating no difference in DSB repair rate among cell types or between locations in the gland (BC in TEB, 0.0062 ± 0.0099; BC in subtending duct, 0.013 ± 0.026; LPC in TEB, 0.0088 ± 0.0107; LPC in subtending duct, 0.014 ± 0.019; LMC in TEB, 0.0093 ± 0.0207; LMC in subtending duct, 0.005 ± 0.010; mean ± SD) (Figs 3A and B and 4).