ATM and breast cancer: Separate analyses of the 15 families carrying the ATM c.7271T > G variant found that this variant increased breast cancer risk by a factor of 8.0 (95% CI, 2.3 to 27.4; P = 0.0005) compared with 4.4 (95% CI, 0.70 to 28.1; P = 0.053) for families with other variants.