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Number of Pregnancies May Influence Breast Cancer Risk in Women With BRCA Mutations

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Key Points

  • Women with BRCA1 mutations who had 2, 3, 4, or more full-term pregnancies were at 21%, 30%, and 50% decreased risk of breast cancer, respectively, compared to women with a single full-term pregnancy. Breastfeeding also reduced risk in BRCA1 mutation carriers.
  • Women with BRCA2 mutations did not have a decreased risk from multiple pregnancies, except if they had four or more pregnancies. 

Researchers have found the lower risk of breast cancer associated with multiple pregnancies and breastfeeding in the general population extends to those at the highest risk of breast cancer. These results were published by Terry et al in the JNCI Cancer Spectrum.

Methods and Findings

The study followed 5,707 BRCA1 and 3,535 BRCA2 mutation carriers in a retrospective cohort and 2,276 BRCA1 and 1,610 BRCA2 mutation carriers in a prospective cohort. Women with BRCA1 mutations who had 2, 3, 4, or more full-term pregnancies were at a 21%, 30%, and 50% decreased risk of breast cancer, respectively, compared to women with a single full-term pregnancy. Breastfeeding also reduced risk in BRCA1 mutation carriers. In contrast, women with BRCA2 mutations did not have a decreased risk from multiple pregnancies, except if they had four or more pregnancies. 

“What we have learned is that timing really matters for many risk factors, and the dual effect of pregnancy we see in nonmutation carriers with a long-term protection but short-term increase following a pregnancy may not extend to all women with BRCA1 and BRCA2 mutations…. The short-term increase and long-term protection may relate much more to the timing of when these pregnancies occur,” said lead author Mary Beth Terry, PhD, Professor of Epidemiology and Environmental Health Sciences at the Mailman School of Public Health at Columbia University and the Herbert Irving Comprehensive Cancer Center, New York. 

“Moreover, the hormonal upheaval that occurs during the first pregnancy may have a more or less important impact on the risk of breast cancer, depending on whether the first pregnancy occurs during periods of life at higher risk of developing a breast cancer or at less high risk,” said senior author Nadine Andrieu, PhD, Director of Research at the Institut National de la Santé et de la Recherche Médicale and the Institut Curie, Paris.

She added, “[These time] periods shifted by about 10 years between BRCA2 and BRCA1 mutation carriers, with a later peak for BRCA2 mutation carriers.”

Disclosure: A full list of funding and the study authors' full disclosures can be found at academic.oup.com.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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