Mimicking Pregnancy To Reduce Breast Cancer Risk

Abstract

Women who have a full-term pregnancy before their mid-20s substantially reduce their lifetime risk of breast cancer, compared with women who either have children later in life or do not have children, according to many epidemiological studies. Women who breastfeed their babies further reduce that risk. Now breast cancer researchers are asking whether those observations can be transformed into a feasible breast cancer prevention strategy. Some investigators contend that the goal should be at the forefront of breast cancer research, whereas others express concern that pregnancy is too complex to mimic. Despite the challenges, several research groups are trying to tackle the question, and a few are even starting to test their hypotheses in women at high risk for breast cancer. Scientists once believed that a woman’s age at her fi rst full-term pregnancy is the most important factor, in terms of pregnancy’s role in breast cancer risk. But recent studies have shown that it plays less of a role than the number of births and duration of breast-feeding, said Valeria Beral, M.D., director of the cancer epidemiology unit at the University of Oxford, during her presentation at the San Antonio Breast Cancer Symposium in December. The role of multiple pregnancies became clear in 2002 when the Collaborative Group on Hormonal Factors in Breast Cancer, an international research group based at the University of Oxford, published a pooled analysis of 47 studies that included approximately 50,000 breast cancer patients and 96,000 healthy women. The team, of which Beral is a member, reported that when they held the age at fi rst birth constant, each birth was associated with a 7% lower relative risk of breast cancer and each 12 months of breastfeeding was associated with a 4.3% lower risk. One can see the association of lower risk and early, multiple pregnancies by comparing the rate of breast cancer in developed and developing countries. The incidence of breast cancer in the United States and Europe is 6.3% among women up to age 70 years. By contrast, the rate is 1.2% in rural Africa and Asia. Although diet and environment may account for some of that difference, the Collaborative Group estimates that the incidence in developed countries could theoretically drop to 2.7% if women adopted the same reproductive patterns as women in developing countries have. Beral is careful to emphasize that no one is