Pregnancy and breastfeeding are known to lessen breast cancer risk, but until now, it wasn’t known whether this risk reduction applied to women at higher risk because of their genes. According to researchers at Columbia University's Mailman School of Public Health in New York who conducted this study, it does indeed.
Women with BRCA1 or BRCA2 genetic mutations are typically at increased risk for breast cancer and ovarian cancer. The Columbia study, published in the Journal of the National Cancer Institute Cancer Spectrum, answers questions about how the number of pregnancies and breastfeeding history may affect a woman’s risk of developing breast cancer if she has one of these mutations. Their study involved more than 5,700 women with BRCA1 gene mutations and 3,500 women with BRCA2 mutations.
In women with BRCA1 mutations, two, three, or four full-term pregnancies lower breast cancer risk by 21 percent, 30 percent, and 50 percent, respectively, compared with women who have the genetic mutation and carry just one pregnancy to term. Four or more full-term pregnancies were also associated with a lower breast cancer risk in women with BRCA2 genetic mutations.
The Columbia researchers also discovered that the timing of the pregnancies is significant. Women with BRCA1 mutations see greater benefits when they’re pregnant or breastfeed younger — in their 20s, for example — and those with BRCA2 mutations experience greater benefits from later-in-life pregnancies. The benefits are believed to be related to fluctuations in hormone levels.