According to the results of a study published in the Journal of the American Medical Association, risk of breast cancer among BRCA1/2 carriers varies across families.
Inherited mutations in two genes-BRCA1 and BRCA2-have been found to greatly increase the lifetime risk of developing breast and ovarian cancer. Mutations in these genes can be passed down through either the mother’s or the father’s side of the family.
To explore whether and how risk of breast cancer varies among women with a BRCA1 or BRCA2 mutation, researchers evaluated breast cancer risk among female first-degree relatives (mothers, sisters, daughters) of breast cancer patients with a BRCA1 or BRCA2 mutation.
Information was available for 598 female first-degree relatives (350 from BRCA1 families and 248 from BRCA2 families).
- Relatives of women who were diagnosed with breast cancer at a younger age were more likely to develop breast cancer themselves. The estimated risk of breast cancer by the age of 70 was 52% for relatives of women diagnosed before the age of 35 and 36% for relatives of women diagnosed between the ages of 45 and 55.
- There was a suggestion that relatives of women who had a second breast cancer diagnosed in the opposite breast (contralateral breast cancer) were more likely to develop breast cancer themselves. The estimated risk of breast cancer was 51% for relatives of women with contralateral breast cancer and 40% for relatives of women with unilateral (one-sided) breast cancer. This difference did not meet the criteria for statistical significance, however, suggesting that it could have occurred by chance alone.
- Even after accounting for factors such as age at diagnosis and presence of contralateral breast cancer, risk of breast cancer varied across BRCA1/2 families.
The researchers conclude that there is broad variation in risk of breast cancer among carriers of BRCA1 and BRCA2 mutations.
Reference: Begg CB, Haile RW, Borg A et al. Variation of breast cancer risk among BRCA1/2 carriers. Journal of the American Medical Association. 2008;299:194-201.