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A new report suggests that breast-feeding, which has been associated with a reduced breast cancer risk, may have another benefit. In mothers who later develop breast cancer, breast-feeding may reduce the risk of cancer recurrence.

The study, in the July issue of The Journal of the National Cancer Institute, followed 1,636 breast cancer survivors. Researchers examined medical records and gathered data on whether mothers had ever breast-fed their children. They found 383 recurrences and 290 breast cancer deaths during an average nine years of follow-up after completion of treatment.

After controlling for age, smoking, education, race, type of therapy and other factors, they found that compared with women who had never breast-fed, any breast-feeding was associated with a 30 percent reduced risk of recurrence, and breast-feeding for more than six months was associated with a 37 percent reduced risk. There were similar risk reductions for breast cancer deaths.

“Breast-feeding is a good thing for the baby, and there are additional benefits for the mom that this study suggests,” said the lead author, Marilyn L. Kwan, a research scientist at Kaiser Permanente in Oakland, Calif. “This contributes to information already available in making a personal decision about whether or not to breast-feed.”

The risk reductions were particularly apparent in estrogen-receptor positive cancers, the most common type, but were not significant for women with HER2 positive tumors. Breast-feeding leads to certain molecular changes in breast cells, which may help explain the effect.