Three per cent of Norwegian ovarian cancers are caused by BRCA1 1675delA or 1135insA

Our aim was to determine the prevalence of two Norwegian BRCA1 founder muta tions in ovarian cancer patients, to identify carriers and their families f or medical follow-up, and to study histopathological factors. Of a cohort o f 727 ovarian cancer patients, 615 gave informed consent to testing. 2.9% ( 18/615) of the tested patients were found to be carriers of BRCA1 1675delA (n = 13) or 1135insA (n = 5). The total frequency of the mutations was 4.7% (8/171) in patients below 50 years of age, and zero (0/144) in patients ab ove 70 years of age. In patients below 70 years of age, the frequency of 16 75delA and 1135insA mutations was 2.8% and 1.0%, respectively. Out of 13 pa tients with 1675delA mutation, 4 had breast cancer. 14/16 (87.5%) families fulfilled clinical criteria for familial breast-ovarian cancer. Median age of onset of ovarian and breast cancer was 51 years and 37 years, respective ly. Mutation carriers tended to have tumours with unfavourable prognostic f actors. This is, to our knowledge, the highest reported frequency of founde r mutations in a national ovarian cancer cohort (less than in the Ashkenazi s). It seems justified to offer such testing to ovarian cancer patients bel ow 70 years of age in Norway, identify their risk of breast cancer and offe r medical follow-up to the families. (C) 1999 Elsevier Science Ltd. All rig hts reserved.