Breast cancer risk increases after childbirth, study says

While scientists do not know what causes cancer, they believe childbirth may increase the possibility of a diagnosis, according to a new report.

Researchers from the University of North Carolina's Lineberger Comprehensive Cancer Center recently conducted a study, published in the Annals of Internal Medicine, to determine the association between the disease and childbirth.

To do so, they gathered data from 15 previous studies that examined a total of 889,944 women. They assessed breast cancer risk after childbirth and considered other factors, including breastfeeding and family history of breast cancer.

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After analyzing the results, they found younger women who have recently had a child may have a higher risk of breast cancer compared to their peers of the same age who do not have children. In fact, the risk for moms 55 and younger was about 80 percent higher and the chances of developing it was highest five years after giving birth. The risk leveled off 23 years after giving birth.

"What most people know is that women who have children tend to have lower breast cancer risk than women who have not had children, but that really comes from what breast cancer looks like for women in their 60s and beyond," co-author Hazel Nichols said in a statement. "We found that it can take more than 20 years for childbirth to become protective for breast cancer, and that before that, breast cancer risk was higher in women who had recently had a child."

Despite their findings, the scientists noted overall risk of breast cancer is still low for mothers after pregnancy. They also discovered their results didn’t apply to all younger women. Risk was higher for women who had their first child after 35, but there was no increased risk of breast cancer after a recent birth for women who had their first child before 25.

“This is evidence of the fact that just as breast cancer risk factors for young women can differ from risk factors in older women, there are different types of breast cancer, and the risk factors for developing one type versus another can differ,” Nichols said.

The authors now hope their investigations will help improve prediction of breast cancer and lead to greater awareness among young mothers.

“There are many ongoing studies that are trying to improve our ability to do breast cancer risk prediction on the individual level,” Nichols concluded. “This is one piece of evidence that can be considered for building new prediction models.”

Cox Media Group