Childbirths and Breast Cancer Risk

April 20, 2006 -- Full-term pregnancypregnancy provides a similar level of protection against breast cancerbreast cancer to women who are genetically predisposed to develop the disease and those who are not, findings from a European study show.

For women who have a child, each additional full-term child that a woman with BRCA 1 and BRCA 2 genetic mutations carried reduced her breast cancercancer risk by 14%, researchers reported. This was limited to women over 40 years of age.

While significant, this risk reduction is small compared with other interventions available to women with BRCA mutations, researcher Douglas F. Easton, PhD, of Cambridge University says.

"These findings can best be used to help us better understand risk among women with BRCA mutations," Easton tells WebMD. "I do not think there are public health implications in terms of instructing at-risk women about reproductive issues."

Up to 80% Lifetime Risk

A woman who carries a BRCA mutation has a 65% to 80% chance of developing breast cancer during her lifetime.

While it is well recognized that childbirth protects against breast cancer in women without a genetic susceptibility to the disease, its impact on BRCA mutation carriers has been less clear.

There has even been some suggestion that pregnancy increases breast cancer risk in women who are genetically predisposed to developing the disease.

In the normal-risk population, the number of children a woman has and the age at which she has them influence breast cancer risk. According to the National Cancer Institute, a woman who has her first child after the age of 35 has roughly twice the risk of developing breast cancer during her lifetime as a woman who gives birth before the age of 20.

In the new study, researcher Nadine Andrieu, of the Institut Curie in Paris, and colleagues wanted to find out if the same association held true for women with BRCA 1 and BRCA 2 mutations.

The researchers retrospectively reviewed interviews with 1,601 women with BRCA mutations enrolled in an international study. About half of the women had been diagnosed with breast cancer.

Additional Births and CancerCancer Risk

Having one child was not associated with a decrease in breast cancerbreast cancer risk. But each additional birth was found to reduce breast cancer risk by 14% in women who were 40 and older when interviewed. The association was the same for carriers of both BRCA 1 and BRCA 2 mutations.

This was not the case, however, when it came to age at first birth. Having a first child after the age of 20 was associated with an increased risk of breast cancer in BRCA 2 mutation carriers. But in BRCA 1 carriers, first childbirth at age 30 and older was associated with a decrease in breast cancer risk compared with first childbirth before age 20.

The researchers concluded that this difference may be due to chance, or that it may reflect a real difference in risk among BRCA 1 and BRCA 2 mutation carriers.

The study is published in the April 19 issue of the Journal of the National Cancer Institute.

Screening and Intervention

Women who are known to be carriers of the BRCA mutation often undergo increased surveillance, and more and more are choosing either drug or surgical interventions to reduce their risk.

Preventive mastectomy to remove breast tissue before a malignancy can develop dramatically reduces breast cancer risk, but it does not eliminate risk. Likewise, surgical removal of the ovaries has been shown to cut breast cancer risk by half in women with BRCA mutations.

American Cancer Society spokesman Len Lichtenfeld, MD, FACP, tells WebMD that genetically susceptible women should consider beginning breast cancer screening at age 30. It is also generally recommended that they get screened every six months, instead of every year.

There is also some debate about how to best screen women with BRCA mutations. Lichtenfeld says magnetic resonance imaging (MRI) and ultrasound are increasingly being used instead of mammography to screen high-risk, younger women because these techniques are believed to be more effective for identifying cancers in denser breasts.

Lichtenfeld says the newly published study should reassure high-risk women that pregnancypregnancy will not increase their risk of developing breast cancer.

SOURCES: Andrieu, N. Journal of the National Cancer Institute, April 19, 2006; vol. 98: pp. 535-544. Douglas F. Easton, PhD, professor of genetics, department of public health and primary care, University of Cambridge, U.K. Len Lichtenfeld, MD, FACP, deputy chief medical officer, American Cancer Society. NCI Pregnancy and Breast Cancer Risk Fact Sheet. American Cancer Society web site.