Breastfeeding reduced breast cancer risk in women with family history of the disease

Women with a family history of breast cancer who breastfed their children had a 59% reduced risk for breast cancer, according to the results of a prospective cohort study of parous women in the Nurses’ Health Study II.

Prior research examining the link between breastfeeding and reduced breast cancer risk has been largely inconclusive, according to researchers. This large study examined detailed information on lactation history, supplemental feeding, and lactation amenorrhea in 60,075 women from NHS II from 1997 to 2004. Eighty-seven percent of women had ever breastfed.

The researchers identified 608 cases of premenopausal breast cancer during 357,556 person-years of follow-up. There was a lower incidence of breast cancer among women who had breastfed compared with women who had not (HR=0.75; 95% CI, 0.56-1.00). No association was found for the duration of breastfeeding.

The relationship between breastfeeding and a reduced risk of breast cancer was even greater among women with a first-degree relative with the disease (P=.03), according to researchers. Women with family history of breast cancer who breastfed were less than half as likely to develop breast cancer compared with women who had not breastfeed (HR=0.41; 95% CI, 0.22-.075).

No trend was found for duration of total lactation, exclusive lactation or lactation amenorrhea, and no association was noted among women who had no family history of breast cancer.

“The observed 59% reduction in risk compared favorably with hormonal treatments such as tamoxifen for women at high risk for breast cancer,” the researchers wrote. “Moreover, breastfeeding is associated with multiple other health benefits for both mother and child."

Stuebe AM. Arch Intern Med. 2009;169:1364-1371.

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