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Breast cancer risk after childbirth may persist more than 20 years

The increased risk for breast cancer after giving birth can last for around 24 years, according to findings published in Annals of Internal Medicine.

“Parity is widely recognized as protective for breast cancer, but breast cancer risk may be increased shortly after childbirth,” Hazel B. Nichols, PhD, assistant professor in the department of epidemiology at the University of North Carolina Gillings School of Global Public Health, and colleagues wrote. “Whether this risk varies with breastfeeding, family history of breast cancer, or specific tumor subtype has rarely been evaluated.”

Nichols and colleagues analyzed data from 15 prospective cohort studies to examine the risk for breast cancer after recent childbirth. The researchers included 889,944 women aged younger than 55 years (mean age, 41.8 years) without breast cancer at enrollment.

Among all participants, 720,555 were parous at enrollment and 71,609 more had given birth during follow-up. Pregnancy information was finalized at a mean age of 50 years.

The increased risk for breast cancer after giving birth can last for around 24 years.

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The researchers identified 18,826 incident cases of breast cancer.

The risk for breast cancer peaked around 5 years after birth among women who had given birth (HR = 1.8; 95% CI, 1.63-1.99) and continued for 24 years, compared with those who had never given birth. After 34 years, the HR decreased to 0.77 (95% CI, 0.67-0.88) in parous women.

The increased risk for breast cancer after giving birth was mainly fueled by estrogen receptor-positive breast cancer. There was no observed pattern for estrogen receptor-negative breast cancer.

Women who were older at first birth, had multiple births or a family history of breast cancer had a greater increased risk for breast cancer. Breastfeeding did not affect breast cancer risk.

These findings suggest that “health care providers should consider recent childbirth a risk factor for breast cancer in young women,” Nichols and colleagues concluded. – by Alaina Tedesco

Disclosures: Nichols reports no relevant financial disclosures. Please see study for all other authors’ relevant financial disclosures.