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Breastfeeding associated with reduced risk of breast cancer among women with family history

The JAMA Network Journals

Women with a family history of breast cancer appear to have a lower risk of developing the disease before menopause if they have ever breastfed a child, according to a report in the August 10/24 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

More women around the world develop breast cancer than any other malignancy, according to background information in the article. Established risk factors include a family history, beginning menstruation at an early age and not having children or having a first child at a late age.

Alison M. Stuebe, M.D., M.Sc., then of Brigham and Women's Hospital and Harvard Medical School, Boston, and now of the University of North Carolina at Chapel Hill, and colleagues used information from 60,075 women who had given birth and who participated in the Nurses' Health Study between 1997 and 2005. Each woman completed a detailed questionnaire on demographic characteristics, body measurements and lifestyle factors, with follow-up questionnaires every two years. Breastfeeding history was assessed in detail on the 1997 questionnaire, and on each subsequent follow-up the women were asked to report whether they had been diagnosed with breast cancer.

Through the end of the study--June 2005--a total of 608 cases of premenopausal breast cancer were diagnosed, at an average age of 46.2 years. Women who had a first-degree relative with breast cancer had a lower risk of developing the disease if they had ever breastfed than if they had never breastfed. The association did not appear to change based on duration of breastfeeding, whether breastfeeding was exclusive or whether the woman experienced amenorrhea (absence of menstruation) as a result. There was no association between breastfeeding and breast cancer among women without a family history.

Women who did not breastfeed but used medication to suppress breast milk production also appeared to have a lower risk of breast cancer than women who neither breastfed nor used lactation suppression. This association could be related to disordered involution, or a malfunction in the process by which mammary tissue returns to its pre-pregnant state caused by engorgement and inflammation, the authors note.

"Future studies of interactions among breastfeeding history, family history and genotypes associated with breast cancer risk will be needed to confirm these associations and explore underlying mechanisms," they write. In the meantime, the observed risk reduction compared favorably to that experienced by high-risk women taking hormonal treatments such as tamoxifen, they continue. "Moreover, breastfeeding is associated with multiple other health benefits for both mother and child. These data suggest that women with a family history of breast cancer should be strongly encouraged to breastfeed."

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(Arch Intern Med. 2009;169[15]:1364-1371. Available pre-embargo to the media at www.jamamedia.org.)

Editor's Note: The Nurses' Health Study II is supported by a Public Health Service grant from the National Cancer Institute, National Institutes of Health, U.S. Department of Health and Human Services. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

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