Women who wait to have babies later in life are less likely to develop an aggressive form of breast cancer than younger-age mothers, new research suggests.
Health scientists with the Fred Hutchinson Cancer Research Center found delaying childbirth 15 years or more after starting menstruation reduces risk of what’s known as triple-negative breast cancer — a particularly virulent form of the disease that is difficult to treat — by up to 60 percent
"We found that the interval between menarche and age at first live birth is inversely associated with the risk of triple-negative breast cancer," said Christopher I. Li, M.D., a member of the Public Health Sciences Division at Fred Hutch who helped conduct the study, published online in the journal Breast Cancer Research and Treatment.
"Our observations that delayed childbearing and breast-feeding are protective against triple-negative breast cancer suggest that variations in reproductive histories by race may to some extent explain the higher rates of triple-negative disease in African-American women," Dr. Li said.
The study is the first to examine the connection between early childbirth and triple-negative breast cancer, which accounts for up to 20 percent of all breast cancers. Unlike other forms of the disease, this type of breast cancer does not depend on hormones such as estrogen to grow and spread, and as a result does not respond to hormone-blocking drugs such as Tamoxifen.
The study involved more than 1,960 Seattle-area women — 20 to 44 years of age — about half of whom had a history of breast cancer. Researchers compared the women’s histories of breast cancer and childbirth and found delaying childbirth reduced the risk of breast cancer for reasons that are unclear, Dr. Li said.
Dr. Li said the findings have particular implications for African-American women, who have higher rates of triple-negative breast cancer than others, are more likely to start having children at a younger age, and are less likely to breast-feed.
The study was funded by the National Cancer Institute and the Department of Defense Breast Cancer Research Program.