BRCA1 and breast cancer: Today we estimate that the genetic component of breast cancer represents 5% to 10% of all breast cancers, with 4% to 5% due to high-penetrance mutations in susceptibility genes[3–5] Mutations in two high-penetrance susceptibility genes have been identified: BRCA1 and BRCA2. Pathogenic mutations in BRCA1 confer a lifetime risk of BC of 60% to 85%[6,7], whereas such mutations in BRCA2 confer a lifetime risk of approximately 40% to 85%[6,7].