BRCA1 and breast cancer: The gene that contributed most to risk was BRCA1, both because 7.0% of patients (80 of 1,136) harbored a damaging mutation in BRCA1 and because the increase in breast cancer risk associated with BRCA1 mutation was extremely high (OR, 23.40; 95% CI, 7.41 to 73.88; P < .001).