For acquisition of control specimens, samples already collected under IRB approved protocol 99-030 will be used. This protocol was a tissue and blood acquisition protocol entitled "Collection of Tissue, Blood, and Cells to Be Used for Studying the Causes, Prevention, Diagnosis, and Treatment of Breast Cancer". Patients have already given consent and signed a research authorization for to use their blood specimens for this purpose. Controls will also be collected from patients who have previously undergone genetic counseling through the Clinical Genetics Service at MSKCC and tested negative for a germline mutations in BRCA1. These individuals will be approached and asked to donate a sample at the time of their results appointment. Blood samples from cases will be collected from patients who have tested positive for a germline mutation in BRCA1. These women will have been participants in MSKCC protocols such as 96-51 and 97-29, or tested at outside institutions and receiving followup care at MSKCC. Any patient with a presumed pathogenic mutation in BRCA1 will be eligible for inclusion.