Delaying childbirth by 15 years after menarche may lower the odds of an aggressive form of breast cancer by 60%, says a new 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," said Christopher I. Li, member of Public Health Sciences Division at Fred Hutchinson Cancer Research Centre, who led the study.
The study involved more than 1,960 Seattle-area women between the ages of 20 and 44, 1,021 with a history of breast cancer and 941 without, the journal Breast Cancer Research and Treatment reports.
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% of all breast cancers, does not respond to hormone-blocking drugs such as Tamoxifen, according to a Fred Hutchinson statement.
The study by Li and colleagues is the first to look at how the interval between first menstrual period and age at first birth is related to the risk of this particular type of breast cancer.
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.