A prospective cohort study of 1305 BRCA1 positive and 908 BRCA2 positive breast cancer patients found that the risk of CBC 20 years after initial breast cancer was 40% for BRCA1 and 26% for BRCA2. The younger the age of onset of the first breast cancer, the higher the risk of CBC [64]. This evidence concerns the gene BRCA1 and breast cancer.