Introduction

The awareness of genetic predisposition to breast cancer has increased tremendously since the identification of the two highly penetrant breast and ovarian cancer genes – BRCA1 and BRCA2 (Miki et al., 1994; Wooster et al., 1995). Women with a family history of breast cancer are particularly concerned about their own risk, thus creating a greater demand for risk assessment and genetic counselling as well as for genetic testing. Mutations in BRCA1 or BRCA2 account for the majority of high-risk families in which the segregation of a dominant high-penetrance susceptibility gene has quite clearly manifested itself in multiple cases of breast cancer over several generations of close relatives (Ford et al., 1998). Only a small proportion of families with a less striking family history and isolated early-onset breast cancer can also be attributed to mutations in these genes (Frank et al., 1998; Malone et al., 1998; Newman et al., 1998) except in founder populations with recurrent mutations (Andersen et al., 1996; Johannesdottir et al., 1996; Fodor et al., 1998; Thorlacius et al., 1998). Screening for mutations is, however, still a technically demanding and labour-intensive task, and gene testing is usually only offered to persons with a greater than three-fold increase in risk compared with the general population (Gayther and Ponder, 1997). Generally, for genetic counselling on familial breast cancer, an accurate evaluation is needed of the probability that a woman carries a mutation before any decisions are made regarding genetic testing.