From Our 2010 Archives

Long-Term Breastfeeding Tied to More Aggressive Cancers

FRIDAY, March 26 (HealthDay News) -- Women who breastfeed for six months or more face a higher risk of developing the most aggressive types of breast cancer, but it's not clear whether there's a cause-and-effect relationship, a new study finds.

Researchers also don't know if these women are more likely to die of cancer than others. Overall, breastfeeding is thought to reduce the risk of breast cancer.

Dr. Salma Butt, of Malmö University Hospital in Sweden, and colleagues examined statistics from a study of 17,035 women and focused on 622 who developed breast cancer. They also looked at how those women handled breastfeeding for their children.

"We found a statistically significant risk of grade [3] tumors in women with an average time of breastfeeding of 6.2 months or more," she said in a news release.

"The biological mechanisms behind this are still to be identified," Butt said. "What is known is that breastfeeding reduces the number of ovulatory menstrual cycles over a lifetime, thereby reducing the impact of hormone levels present during normal menstrual cycles and, in particular, reducing the progesterone exposure. This may explain the finding in previous studies of a reduced risk of breast cancer in women who had breastfed."

"However, breastfeeding stimulates the production of prolactin, a hormone that has been reported to have tumor-promoting effects," she said. "But the relation between breastfeeding, prolactin and breast cancer is complex and not fully understood."

The findings were to be presented Friday at the European Breast Cancer Conference in Barcelona, Spain.

Butt said the findings shouldn't discourage women from breastfeeding. Rather, women thought to be at high risk for aggressive tumors could be screened, Butt said.

-- Randy Dotinga

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SOURCE: European Breast Cancer Conference, news release, March 26, 2010