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Breastfeeding and Cancer in High-Risk Women

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

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.

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