Breast cancer risk and hormone receptor status in older women by parity, age of first birth, and breastfeeding: A case-control study

Sarah J. Lord, Leslie Bernstein, Karen A. Johnson, Kathleen E. Malone, Jill A. McDonald, Polly A. Marchbanks, Michael S. Simon, Brian L. Strom, Michael F. Press, Suzanne G. Folger, Ronald T. Burkman, Dennis Deapen, Robert Spirtas, Giske Ursin

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


Background: Early age at first birth and multiparity reduce the risk of estrogen receptor-progesterone receptor (ERPR)-positive breast cancer, whereas breastfeeding reduces the risk of both ERPR-positive and ERPR-negative cancers. Methods: We used multivariable logistic regression analysis to investigate whether age at first birth (<25 or ≥25 years) and breastfeeding (ever/never) modify the long-term effect of parity on risk of ERPR-positive and ERPR-negative cancer using 1,457 incident breast cancer cases and 1,455 controls ages ≥55 years who participated in the Women's Contraceptive and Reproductive Experiences Study. Results: Women who gave birth before age 25 years had a 36% reduced risk of breast cancer compared with nulligravida that was not observed for women who started their families at an older age (P heterogeneity = 0.0007). This protective effect was restricted to ERPR-positive breast cancer (Pheterogeneity = 0.004). Late age at first birth increased the risk of ERPR-negative cancers. Additional births reduced the risk of ERPR-positive cancers among women with an early first birth (Ptrend = 0.0001) and among women who breastfed (Ptrend = 0.004) but not among older mothers or those who never breastfed. In women with a late first birth who never breastfed, multiparity was associated with increased risk of breast cancer. Conclusions: These findings suggest that the effect of parity on a woman's long-term risk of breast cancer is modified by age at first full-term pregnancy and possibly by breastfeeding.

Original languageEnglish (US)
Pages (from-to)1723-1730
Number of pages8
JournalCancer Epidemiology Biomarkers and Prevention
Issue number7
StatePublished - Jul 2008
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Epidemiology
  • Oncology


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