Objective: Our purpose was to determine the frequency of allele loss in the region of the BRCA1 gene in cancers of women who have both breast and ovarian cancer.
Study design: Four polymorphic microsatellite markers on chromosome 17q11-21 were examined by the polymerase chain reaction in deoxyribonucleic acid from paraffin blocks of normal tissues, breast cancers, and ovarian cancers in 24 women who had primary cancers in both sites.
Results: Loss of heterozygosity was seen in one or more markers on chromosome 17q11-21 in 46% of breast cancers and 78% of ovarian cancers. In 38% of cases allele loss was seen in both cancers, and in all these cases the same allele was lost in both cancers. Significantly younger ages at diagnosis of both breast and ovarian cancer were noted among cases with allele loss in both cancers compared with cases in which allele loss was found only in the ovarian cancer (p < 0.05).
Conclusions: Because cases in which 17q11-21 allele loss was seen in both cancers had a young age of onset and the same allele was always deleted in both cancers, hereditary alterations in BRCA1 may play a role in this subset. The older age of onset in cases in which allele loss was seen only in the ovarian cancer suggests that the development of these cancers is not related to an inherited defect in BRCA1.