Childbirth tied to later risk for breast cancer

  • Nichols HB & al.
  • Ann Intern Med
  • 11 Dec 2018

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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Takeaway

  • Parous women may have elevated risk for breast cancer (BCa) for 23.6 years after childbirth compared with nulliparous women, with the risk peaking at 5 years, according to a pooled analysis of 15 prospective cohort studies.
  • The effect is driven by estrogen receptor-positive (ER+) BCa.
  • Breastfeeding has no effect on risk.

Why this matters

  • Recent childbirth should be viewed as a risk factor for BCa.

Study design

  • Pooled analysis of individual-level data from 15 prospective cohorts (n=889,944) of premenopausal women in the international Premenopausal Breast Cancer Collaborative Group.
  • Funding: Avon Foundation; NIH; others.

Key results

  • Mean follow-up, 10.8 years; 18,826 incident BCa cases diagnosed before 55 years of age.
  • Parity (vs nulliparity) was associated with increased BCa risk that lasted 23.6 years, peaking at 4.6 years after birth (HR, 1.80; 95% CI, 1.63-1.99).
    • Effect was driven by ER+ BCa, which accounted for 76% of all cases.
  • The combination of parity and family history was associated with an even larger increase in risk peaking at 4.9 years (HR, 3.53; 95% CI, 2.91-4.29).
  • Parity gradually switched to a protective factor that reached its lowest observed point at 34.5 years after birth (HR, 0.77; 95% CI, 0.67-0.88).
  • Breastfeeding had no effect on BCa risk.

Limitations

  • Observational design.

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