BRCA1 and breast cancer: For instance, after 25 years 55.1% (95%CI, 45.4% to 64.9%) of patients from BRCA1 positive families, 38.4% (95% CI, 18.5% to 58.2%) of patients from BRCA2 families and 28.4% (95% CI, 20.5% to 36.3%) of patients from non-BRCA1/2 families who were younger than 40 years at first breast cancer developed contralateral breast cancer.