BRCA1 and breast cancer: Only approximately 50% of all familial breast cancers can be explained by known genetic factors, including mutations in BRCA1 and BRCA2. One of the most extensively studied candidates for breast and/or ovarian cancer susceptibility is BARD1. Although it was suggested that large mutations may contribute substantially to the deleterious variants of BARD1, no systematic study of the large mutations in BARD1 has been performed.