Breast-feeding reduced the risk for estrogen receptor-negative and progesterone receptor-negative breast cancer, according to results presented at the 11th Annual AACR International Conference on Frontiers in Cancer Prevention Research, held in Anaheim, Calif., Oct. 16-19, 2012.

“We found an increased risk for estrogen receptor- and progesterone receptor- (ER/PR) negative breast cancer in women who do not breast-feed, but in women who have children and breast-feed, there is no increased risk,” said Meghan Work, M.P.H., doctoral student in the department of epidemiology at Columbia University’s Mailman School of Public Health in New York, N.Y.
Work and colleagues examined the relationship between reproductive risk factors — such as the number of children a woman delivers, breast-feeding and oral contraceptive use — and ER/PR-negative breast cancer. ER/PR-negative breast cancer often affects younger women and has a poor prognosis, according to Work.
The researchers used data from three sites of the Breast Cancer Family Registry, which includes women with and without breast cancer from the United States, Canada and Australia. This study included 4,011 women with breast cancer and 2,997 population-based controls.
The results indicated that having three or more children without breast-feeding was associated with an increased risk for ER/PR-negative breast cancer.
“Women who had children but did not breast-feed had about 1.5 times the risk for ER/PR-negative breast cancer when compared with a control population,” Work said. “If women breast-fed their children, there was no increased risk for ER/PR-negative cancer.”
Further, the researchers found that oral contraceptive use was not associated with ER/PR-negative cancer risk, with the exception of those formulations available before 1975. “These earlier formulations contained higher doses of estrogen and progestin than more recent versions,” Work said.
These findings are in line with previous findings that have demonstrated breast-feeding benefit in triple-negative breast cancer. “This is particularly important as breast-feeding is a modifiable factor that can be promoted and supported through health policy,” Work said.

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