Abstract
The breast-ovary cancer-family syndrome is a dominant predisposition to cancer of the breast and ovaries which has been mapped to chromosome region 17q12-q21. The majority, but not all, of breast-ovary cancer families show linkage to this susceptibility locus, designated BRCA1. We report here the results of a linkage analysis of 145 families with both breast and ovarian cancer. These families contain either a total of three or more cases of early-onset (before age 60 years) breast cancer or ovarian cancer. All families contained at least one case of ovarian cancer. Overall, an estimated 76% of the 145 families are linked to the BRCA1 locus. None of 13 families with cases of male breast cancer appear to be linked, but it is estimated that 92% (95% confidence interval 76%-100%) of families with no male breast cancer and with two or more ovarian cancers are linked to BRCA1. These data suggest that the breast-ovarian cancer-family syndrome is genetically heterogeneous. However, the large majority of families with early-onset breast cancer and with two or more cases of ovarian cancer are likely to be due to BRCA1 mutations.