Childbirth may increase risk of breast cancer
Parous vs nulliparous women have a higher risk for breast cancer that persists for more than 20 years after childbirth, a recent study has shown.
“Healthcare providers should consider recent childbirth a risk factor for breast cancer in young women,” the investigators said.
The hazard ratio (HR) for breast cancer among parous vs nulliparous women peaked about 5 years after childbirth (HR, 1.80; 95 percent CI, 1.63–1.99) before decreasing to 0.77 (0.67–0.88) after 34 years. This association shifted from positive to negative about 24 years after childbirth.
Oestrogen receptor (ER)–positive breast cancer was the driver of the overall pattern. There was no crossover for ER-negative cancer.
The risk of breast cancer after childbirth increased when combined with a family history of breast cancer and were higher for women who were older at first birth or who had more births. Additionally, breastfeeding appeared to have no impact on overall risk patterns.
The study was limited by breast cancer diagnoses during pregnancy that were not uniformly distinguishable from early postpartum diagnoses. In addition, there was also limited data on human epidermal growth factor receptor 2 oncogene overexpression.
To characterize breast cancer risk in relation to recent childbirth, a pooled analysis was performed on individual-level data from 15 prospective cohort studies involving women <55 years. A total of 18,826 incident cases of breast cancer were diagnosed during 9.6 million person-years of follow-up. Cox proportional hazards regression was used to calculate HRs and 95 percent CIs for breast cancer.
“Parity is widely recognized as protective for breast cancer, but breast cancer risk may be increased shortly after childbirth. Whether this risk varies with breastfeeding, family history of breast cancer or specific tumour subtype has rarely been evaluated,” the investigators said.