AGE AT DIAGNOSIS AS AN INDICATOR OF ELIGIBILITY FOR BRCA1 DNA TESTINGIN FAMILIAL BREAST-CANCER

We searched for criteria that could indicate breast cancer families wi th a high prior probability of being caused by the breast/ovarian canc er susceptibility locus BRCA1 on chromosome 17. To this end, we perfor med a linkage study with 59 consecutively collected Dutch breast cance r families, including 16 with at least one case of ovarian cancer. We used an intake cut-off of at least three first-degree relatives with b reast and/or ovarian cancer at any age. Significant evidence for linka ge was found only among the 13 breast cancer families with a mean age at diagnosis of less than 45 years. An unexpectedly low proportion of the breast-ovarian cancer families were estimated to be linked to BRCA 1, which could be due to a founder effect in the Dutch population. Giv en the expected logistical problems in clinical management now that BR CA1 has been identified, we propose an interim period in which only fa milies with a strong positive family history for early onset breast an d/or ovarian cancer will be offered BRCA1 mutation testing.