For women who do not have a BRCA1 or BRCA2 gene mutation, having a close relative with one of these mutations does not increase breast cancer risk. These results were published in the Journal of Clinical Oncology.
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.
Women who test negative for a BRCA gene mutation—but who have family members with a mutation—are generally thought to have a risk of breast cancer that’s similar to that of women in the general population. A study published in 2007, however, raised concerns that relatives of BRCA mutation carriers may have a substantially increased risk of breast cancer even if they test negative for their family’s mutation.
To further explore cancer risk among close relatives of people with BRCA mutations, researchers conducted a study among more than 3,000 families with at least one case of breast cancer; 160 families had a BRCA1 mutation and 132 families had a BRCA2 mutation.
For women without a BRCA mutation, breast cancer risk was similar whether or not the woman’s family had a BRCA mutation. These results suggest that coming from a family with a BRCA1 or BRCA2 gene mutation does not increase cancer risk for those who test negative for the mutation.
Although this is reassuring news, women who test negative for their family’s gene mutation should continue to follow cancer screening guidelines. These women do not have the very elevated cancer risk that their affected relatives have, but they can still get cancer.
 Smith A, Moran A, Boyd MC et al. Phenocopies in BRCA1 and BRCA2 families: evidence for modifier genes and implications for screening. Journal of Medical Genetics. 2007;44:10-15.
 Kurian AW, Gong GD, John EM et al. Breast cancer risk for noncarriers of family-specific BRCA1 and BRCA2 mutations: findings from the Breast Cancer Family Study. Journal of Clinical Oncology. Early online publication October 31, 2011.