Younger women who wait at least 15 years after their first menstrual period to give birth to their first child may reduce their risk of an aggressive form of breast cancer by up to 60 percent, according to a Fred Hutch study.
“We found that the interval between menarche and age at first live birth is inversely associated with the risk of triple-negative breast cancer,” Dr. Christopher Li said.
Dr. Christopher Li
While relatively uncommon, triple-negative breast cancer is a particularly aggressive subtype of the disease that does not depend on hormones such as estrogen to grow and spread. This type of cancer, which accounts for only 10 to 20 percent of all breast cancers, does not express the genes for estrogen receptor (ER), progesterone receptor (PR) or HER2/neu and therefore does not respond to hormone-blocking drugs such as Tamoxifen.
The study also confirmed several previous studies that have suggested that breast-feeding confers a protective effect against triple-negative disease.
“Breast-feeding is emerging as a potentially strong protective factor against one of the most aggressive forms of breast cancer,” Li said.
The mechanism by which breast-feeding and delaying childbirth reduces the risk of this form of breast cancer is unclear, Li said.
The study has particular implications for African-American women, who experience disproportionately high rates of triple-negative disease. While the reason for this remains largely unknown, reproductive characteristics are known to vary by race, and compared to non-Hispanic white women, African-American women are more likely to start having children at a younger age and are less likely to breast-feed, Li said.
“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.”
Li said the findings were based on an observational study, one of the first to focus on premenopausal breast cancer; results require confirmation and should be interpreted with some caution.