Breastfeeding and Cancer in High-Risk Women

Breast Cancer Risk Cut by Almost Half in At-Risk Women Who Breastfeed

By Salynn Boyles 
WebMD Medical News Reviewed By Brunilda Nazario, MD 
July 20, 2004

July 20, 2004 Women at a very high risk of breast cancer -- those with the BRCA1 mutations -- get greater protection from the disease by breastfeeding than lower-risk women.

Breastfeeding for one year or more was associated with a 45% reduction in breast cancer risk among women with the genetic mutation who participated in a new study. In contrast, a 4% reduction in risk was seen among women who breastfed for one year in a study published two years ago.

However, breastfeeding did not appear to protect women with another genetic mutation associated with a very high risk of breast cancer known as BRCA2.

"The differences between women with BRCA1 and BRCA2 mutations may reflect underlying differences in the pathogenesis of cancers associated with the two genes," the researchers wrote in the July 21 issue of the Journal of the National Cancer Institute. "However, because our sample of women with BRCA2 mutations was small, it is premature to conclude that a modest reduced risk is not present in this subgroup as well."

Up to 90% Lifetime Risk

Each year, more than 180,000 women in the U.S. are diagnosed with breast cancer. A few genetic mutations increase the risks of breast cancer, and approximately 10% of breast cancer cases are related to these genetic mutations. Mutations in BRCA1 and BRCA2 genes are involved in up to 70% of all inherited breast cancers.

The lifetime risk of developing breast cancer is as high as 90% among women with BRCA mutations.

In this study, researchers drew from a BRCA database to find roughly 1,000 women with the mutation who had been diagnosed with breast cancer and an equal number of women who also have the mutation but do not have a history of the disease. Information on pregnancies and breastfeeding practices was obtained from a questionnaire administered to the women while they were undergoing genetic counseling.

The researchers reported that among women with BRCA1 mutations, those who developed breast cancer breastfed for an average of six months, compared to almost nine months for women who did not develop breast cancer.

"Our data support the hypothesis that hormonal and reproductive factors modify the risk of breast cancer among women with BRCA1 mutations," researcher Seven A. Narod, MD, and colleagues write.

Does Protection Last?

Co-author Henry T. Lynch, MD, tells WebMD that the failure to see a protective benefit in women with BRCA2 mutations is not too surprising.

"We tend to talk glibly about these two genes as if they were one in the same, but they are very different," he says. "BRCA2 mutation gives rise to a much larger spectrum of cancers. It very well may be that the protective benefits (of breastfeeding) don't extend to women with this mutation."

American Cancer Society spokeswoman Heather Spencer Fiegelson, PhD, tells WebMD that while the study is intriguing, it did not follow the women long enough to determine if breastfeeding conveyed lifelong protection against breast cancer.

The average age at diagnosis was 39 for the breast cancer patients in the study, and many of the women are still in their 40s and 50s.

"It will be interesting to see what happens to these women as they reach their 70s," Spencer Fiegelson says. "It is not yet clear if this is a transient effect or if it is long-lasting."


Jernstrom, J. Journal of the National Cancer Institute, July 21, 2004; vol 96: pp 1094-1098. Henry Lynch, MD, professor and chairman, department of preventive medicine, Creighton University School of Medicine. Heather Spencer Feigelson, PhD, senior epidemiologist, American Cancer Society. Steven A. Narod, MD, Centre for Research in Women’s Health, Toronto.