Reproductive History
Does reproductive history affect the risk of breast cancer?
Women who begin their families at a younger age have a lower risk of breast cancer, probably because, over their lifetime, they have a lower exposure to estrogen than women who don't have children. Those with larger families also get breast cancer less frequently than those with smaller families, at least after menopause.
During the premenopausal years, a woman who gives birth is at a slightly higher risk of breast cancer in the years following the birth. That increased risk decreases with time. By the time she has reached her mid-sixties, a woman who has delivered a single child has a 10% lower chance of getting breast cancer than a woman who remains childless throughout her life. Women who have delivered more children have an even lower risk.
Around half of all American women have had at least one child by age 25. The decision to begin (or not to begin) a family at that age can be based on many personal factors. The choice has little or no effect on the lifetime risk of breast cancer.
Does having a miscarriage or an induced abortion affect the risk of breast cancer?
This is very unlikely. Several research studies suggested that uncompleted pregnancies (those that are terminated by either miscarriage or induced abortion) may result in a slightly higher risk of breast cancer in later life. However, follow-up studies did not show this to be true. A larger number of studies that included many thousands of women did not find an association between uncompleted pregnancies and the risk of breast cancer: women who had had one or more abortions developed breast cancer at the same rate as women who had never had an abortion. Some of the earlier reports had compared the cancer rates for women with abortions during the teen years with the cancer rates for women of the same age who had given birth. The latter group had a lower rate of breast cancer, whether compared with women who had had abortions or with women who had not become pregnant during the teen years.
Decisions about abortion are generally based on religious, ethical, and medical concerns. The risk of breast cancer should not be a factor in the decision to terminate a pregnancy, as there is no reason to believe that an abortion would affect the likelihood of breast cancer.
Does breast-feeding affect my risk of breast cancer?
Although the evidence on the relationship between breast-feeding and the risk of breast cancer is mixed, the most recent data indicate that breast-feeding decreases risk. This makes sense, because breast-feeding can prolong the time between childbirth and the onset of ovulation, therefore decreasing a woman's total exposure to estrogen.
Research among previous generations of women and in developing nations found that women who breast-fed their children for a long time had lower rates of breast cancer than women who never breast-fed at all. Two large prospective studies, one in the United States and one in Finland, did not find a connection between breast-feeding and the risk of breast cancer. However, the total number of women with cancer who had lactated for more than a few months was small, so differences would be difficult to identify. A more recent population-based study used state cancer registries to enroll 1,180 premenopausal women with children and 2,185 randomly selected controls. For this larger study group, there was a significant association: women who breast-fed for longer periods had fewer cases of early breast cancer.
