Birth control pills associated with breast cancer risk in BRCA1 mutation carriers

Women who carry mutations in the BRCA1 breast cancer susceptibility gene and have a history of oral contraceptive use may have an increased risk of early-onset breast cancer, according to a large-scale study in the December 4 issue of the Journal of the National Cancer Institute.

Women with BRCA1 and BRCA2 mutations have a 50% to 80% lifetime risk of developing breast cancer. This risk may be modified by factors that influence the level of hormones produced by the body. Whether this risk is modified by exogenous hormones, such as oral contraceptives or hormone replacement therapy, is unknown. Long-term oral contraceptive use has been associated with a modest increase in the risk of breast cancer in the general population and a decrease in the risk of ovarian cancer.

To examine whether the use of oral contraceptives is associated with the risk of hereditary breast cancer, Steven A. Narod, M.D., of the Sunnybrook and Women’s College Health Sciences Centre and the University of Toronto, and his colleagues looked at history of oral contraceptive use among 1,311 women with BRCA1 or BRCA2 mutations who had breast cancer and 1,311 mutation carriers without breast cancer. The women were recruited from 52 centers in 11 countries.

Among women with BRCA1 mutations, those who used oral contraceptives for 5 or more years had a 33% increase in the risk of breast cancer, compared with women who had never used oral contraceptives. The risk was also elevated in women who used contraceptives before age 30, women who were diagnosed with breast cancer before age 40, and women who first used oral contraceptives before 1975. In contrast, Narod and his colleagues did not find any increase in breast cancer risk in BRCA2 mutation carriers, but they say that more studies should be done to confirm these findings.

The authors say that for women carrying a BRCA1 mutation, age should be an important consideration when prescribing an oral contraceptive. The new findings suggest that “oral contraceptive use after age 30 is not likely to increase the risk of breast cancer among BRCA1 mutation carriers and can be used safely to reduce the risk of ovarian cancer,” they conclude.

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