NAT2 and breast cancer: Breast cancer risk was significantly increased in women with NAT2 slow polymorphism (RR 1.19; 95% CI, 1.09–1.30), but not in those with NAT2 fast polymorphism (RR 1.00; 95% CI, 0.86–1.17), although the two estimates were not significantly heterogeneous (eFigure 3).