In the 10 years since the identification of the BRCA1 gene, many cancer families have been tested throughout the world, and there is ongoing interest in estimating the cancer risks for women with mutations in this gene. There is some evidence that families with mutations in the central part of BRCA1 (nucleotides 2401 to 4190) have a higher than expected ratio of ovarian to breast cancers, due to a lower than average risk of breast cancer.¹ The absolute and relative risks of breast and ovarian cancers associated with different mutations have been difficult to quantify, in part because of the large number of different mutations in the gene, the rarity of mutations in the general population, and the expense of testing. The majority of established BRCA1 mutations are protein truncating, although a number of deleterious missense mutations have also been identified.²

Poland is ideally suited to the study of the genetic epidemiology of BRCAl mutations because the country is ethnically homogeneous, and because three common BRCA1 mutations comprise 91% of all BRCA1 mutations found in the population.³ Since 1999, we have tested large numbers of …