Allele losses in the region 17q12-21 in familial breast and ovarian cancer involve the wild-type chromosome

A predisposing gene for breast and ovarian cancer has recently been mapped to chromosome 17q12–21. If this gene is a tumour suppressor gene, allele losses would be expected in the tumours of affected family members and the losses should affect the wild–type chromosome, reflecting the need for inactivation of the wild–type allele at the predisposing locus. In four multiple case breast–ovarian cancer families, we have found that in each of nine tumours which showed allele losses, the losses were from the wild–type chromosome. This suggests that the putative ‘breast–ovarian’ cancer gene is indeed a tumour suppressor gene.