Cancer risks for Australian women with a BRCA1 or a BRCA2 mutation

One of the primary purposes of genetic testing for mutations in the BRCA1 and BRCA2 genes in patients with familial breast/ovarian cancer has been to provide accurate advice to at-risk relatives. The provision of such advice has been hampered by a lack of appropriate data regarding the cancer risks. Chen and colleagues recently provided precise estimates of the relative risks of breast and ovarian cancer in almost 2000 kindreds with such mutations ascertained through familial cancer clinics across USA. The baseline incidence of breast cancer is lower in Australia than in North America. The relative risks derived from the study have been combined with Australian baseline incidence data to estimate the absolute short-term and long-term risks of breast and ovarian cancers for Australian carriers of different ages. The results are presented as a series of graphs that may be useful in counselling an unaffected carrier of a specified age. It is of note that the incidence of breast cancer in carriers is high in premenopausal women, but approaches the population incidence in postmenopausal women. Conversely, the incidence of ovarian cancer continues to increase from the age of 40 years. Among carriers of BRCA1 or BRCA2 mutations, the cumulative lifetime risk of developing breast cancer is 50-60% and the equivalent risk of ovarian cancer is 20-40%. An unaffected carrier aged 60 years is at greater risk of developing ovarian cancer than breast cancer. These observations have important implications for genetic counselling and decisions regarding prophylactic surgery.