The inheritance of mutated BRCA1 or BRCA2 genes confer a very high risk for developing breast and ovarian cancers, particularly in women with a family history of these cancers. Genetic testing is usually used to determine if women from cancer families carry mutations. However, genetic testing is complicated and sometimes mutations are missed. Recently new techniques have been used to detect a specific type of mutation (deletions) in these genes that were previously missed by conventional methods. The purpose of this research project is to use these new techniques to screen for mutations in women with breast or ovarian cancer that were previously tested and found 'negative' using standard genetic tests. Our findings will further the understanding of the contribution of BRCA1 and BRCA2 in hereditary cancer. Also, they will impact directly on the management of women at high risk for hereditary breast and ovarian cancer as carriers of mutations have options for cancer detection and prevention.