Publication date: January 2013
Breastfeeding and a later age at first birth may reduce the likelihood of triple-negative breast cancer in young women. These results were published in Breast Cancer Research and Treatment.
Reproductive factors such as age at first menstrual period, age at first birth, number of pregnancies, and duration of breastfeeding have frequently been evaluated in relation to the risk of breast cancer, but relatively few studies have considered specific types of breast cancer. Furthermore, risk factors for premenopausal breast cancer may differ from risk factors for postmenopausal breast cancer, making it important to conduct studies among women of varying ages.
To explore reproductive factors in relation to risk of breast cancer among young women (ages 20 to 44), researchers evaluated information from a study of 1,021 women with breast cancer and 941 women without breast cancer. Of the women with breast cancer, 781 had estrogen receptor (ER)-positive breast cancer, 180 had triple-negative breast cancer, and 60 had HER2-positive breast cancer.
Compared with women with ER-positive breast cancer, women with triple-negative breast cancer tended to be younger and were more likely to be African-American.
Factors that were linked with the risk of triple-negative breast cancer included age at first live birth, interval between first menstrual period and first live birth, and history of breastfeeding. Compared with women whose first live birth occurred at ages 20-24, women whose first live birth occurred at age 30 or later were 50-60% less likely to develop triple-negative breast cancer. A similar relationship was seen with interval between first menstrual period and first live birth: a longer interval was associated with a lower risk of triple-negative breast cancer.
Breastfeeding has previously been reported to reduce the risk of triple-negative breast cancer, and a protective effect was also observed in the current study. Women who breastfed for more than 12 months were half as likely as women who never breastfed to develop triple-negative breast cancer.
These results suggest that breastfeeding and a later age at first birth may reduce the risk of triple-negative breast cancer in young women. A protective effect of breastfeeding has also been reported in other studies.