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BRCA1-2 Mutations Increase Risk of Cancer in Opposite Breast

Among women with breast cancer, those with a BRCA1 or BRCA2 gene mutation are much more likely than other women to develop a second breast cancer in the opposite breast. These results were published in the Journal of Clinical Oncology.

Some women who have been diagnosed with breast cancer will eventually develop a second breast cancer in the opposite breast. This is referred to as a contralateral breast cancer. The risk of a second breast cancer among women who have already had breast cancer is higher than the risk of a first breast cancer among women in the general population.

A factor that may influence the risk of contralateral breast cancer is the presence of BRCA1 or BRCA2 gene mutations. Inherited mutations in these genes—which can be passed down through either the mother’s or the father’s side of the family—have been found to greatly increase the lifetime risk of developing breast and ovarian cancer.

To evaluate the relationship between BRCA1 or BRCA2 mutations and risk of a subsequent contralateral breast cancer, researchers conducted a study among more than 2,000 breast cancer patients, some of whom had been diagnosed with a contralateral breast cancer and some of whom had not. Women were only included in the contralateral breast cancer group if their contralateral cancer was diagnosed at least one year after their initial cancer. All of the women had been diagnosed with their first breast cancer before the age of 55.

All of the study participants were tested for BRCA1 and BRCA2 mutations.

Compared with women without a BRCA1 or BRCA2 mutation, risk of a subsequent contralateral breast cancer was 4.5 times higher among women with a BRCA1 mutation and 3.4 times higher among women with a BRCA2 mutation.

Among women with a BRCA1 mutation, a younger age at the time of initial breast cancer diagnosis increased the likelihood of a subsequent contralateral breast cancer.

Information about risk of a subsequent contralateral breast cancer may help guide breast cancer management among women with BRCA1 or BRCA2 mutations.

Reference: Malone KE, Begg CB, Haile RW et al. Population-based study of the risk of second primary contralateral breast cancer associated with carrying a mutation in BRCA1 or BRCA2. Journal of Clinical Oncology. [early online publication]. April 5, 2010.