Women who are older at their first birth, multiparous, or who have a family history of breast cancer are at increased risk for breast cancer, according to a study published in Annals of Internal Medicine.
An international team of researchers conducted a pooled analysis of the international Premenopausal Breast Cancer Collaborative Group to distinguish the correlation between breast cancer risk and recent childbirth in women younger than 55 years.
A total of 18,826 incident cases of breast cancer were diagnosed in 9.6 million person-years of follow-up. The hazard ratio for breast cancer among parous women compared with nulliparous women was 1.80 at nearly 5 years after birth and dropped to 0.77 after 34 years; the link between cancer and years since childbirth shifted from positive correlation to negative at approximately 24 years.
The investigators noted that the association was influenced by estrogen receptor-positive breast cancer and that no switch in correlation was observed for estrogen receptor-negative breast cancer.
When coupled with a family history of breast cancer, risk after childbirth was evident and more pronounced for women who were older at their first birth or who had multiple births; breastfeeding did not affect the overall risk patterns.
One limitation the investigators mentioned was the lack of data on human epidermal growth factor receptor 2 oncogene overexpression.
“Compared with nulliparous women, parous women have an increased risk for breast cancer for more than 20 years after childbirth,” the authors wrote. “Healthcare providers should consider recent childbirth a risk factor for breast cancer in young women.”
Nichols HB, Schoemaker MJ, Cai J, et al. Breast cancer risk after recent childbirth: a pooled analysis of 15 prospective studies [published online December 11, 2018]. Ann Intern Med. doi: 10.7326/M18-1323