Prevalence of BRCA1 in a hospital-based population of Dutch breast cancer patients

The prevalence of disease-related BRCA1 mutations was investigated in 642 D utch breast cancer patients not selected for family history or age at diagn osis. They were tested for germline mutations in the BRCA1 gene using an as say which detects small deletions and insertions (DSDI), as well as the two major genomic founder deletions present in the Dutch population. Data on f amily history and bilateral breast cancer were obtained retrospectively. Te n protein truncating mutations were detected and one in-frame deletion with an unknown relation to disease risk. Four patients carried the Dutch found er deletion of exon 22. Based on these results the estimated prevalence of breast cancer in the general population in the Netherlands attributable to BRCA1 mutations is 2.1%. Under 40 years-of-age and under 50 years-of-age th is prevalence is 9.5% and 6.4%, respectively. All mutation carriers were un der 50 years-of-age at diagnosis of the first breast cancer, and five did n ot have any relative with breast cancer. The proportions of bilateral breas t cancer in the mutation carriers and noncarriers did not differ from each other. These data indicate that in the general Dutch breast cancer populati on the great majority of BRCA1 mutations will be found in women diagnosed u nder 50 years-of-age. (C) 2000 Cancer Research Campaign.