BRCA1 and breast cancer: However, given that deleterious mutations in these genes account for only 1% to 4% of all breast cancer cases across different populations [2] and that genetic testing and genetic counseling have hitherto been relatively expensive, genetic testing for BRCA1 and BRCA2 has typically been offered only in clinical genetics settings to women who have early-onset breast cancer, and/or to individuals with significant family history of breast and ovarian, or other BRCA-related cancers.