Increased risk for breast cancer after childbirth may last more than 20 years

The increased risk for breast cancer that occurs after childbirth can last more than 20 years. The risk may be enhanced when a woman is older at first birth or has a family history of breast cancer, and is not mitigated by breastfeeding. Findings from pooled analysis of 15 prospective studies are published in Annals of Internal Medicine.

Childbirth is widely recognized as protective against breast cancer, but breast cancer risk has been shown to be increased shortly after childbirth. Just how long this heightened risk lasts and factors that contribute to the risk have rarely been assessed.

Researchers from the University of North Carolina Gillings School of Global Public Health (with co-authors from the Institute of Cancer Research in London and the National Institute of Environmental Health Sciences in North Carolina) analyzed individual-level data from 15 prospective cohort studies to characterize breast cancer risk in relation to recent childbirth. The data showed that compared with women of the same age who had never given birth, women who had given birth had an increased risk for breast cancer that peaked about 5 years after birth and continued for about 24 years after birth. The increased risk was seen for both estrogen receptor (ER) positive and ER negative breast cancer, and breastfeeding did not modify risk patterns.

According to the researchers, these findings show that risk factors for breast cancer can differ between older and younger women, and should be considered in combination with other characteristics than may influence risk, such as a family history of breast cancer. Combined with evidence from other studies, this research may help to develop better breast cancer risk prediction models to inform decision-making around breast cancer screening and prevention strategies.