Pregnancy termination in relation to risk of breast cancer

JAMA. 1996 Jan 24-31;275(4):283-7.


Objective: To evaluate the association between pregnancy terminations and risk of breast cancer.

Design and setting: Population-based case-control study in Wisconsin, Massachusetts, Maine, and New Hampshire.

Study participants: Cases were women younger than 75 years with a new diagnosis of breast cancer (n = 6888), identified from statewide tumor registries. Controls younger than 65 years (n = 9529) were randomly selected from lists of licensed drivers, or for older subjects, from lists of Medicare beneficiaries. EXPOSURES AND OUTCOMES: Breast cancer risk in relation to spontaneous or induced abortions.

Results: After adjustment for parity, age at first birth, and other risk factors, pregnancy termination (induced or spontaneous) was associated with a relative risk (RR) of breast cancer of 1.12 (95% confidence interval [CI], 1.04 to 1.21), compared with the risk among women who had never had a termination. Induced terminations were associated with a RR of 1.23 (95% CI, 1.00 to 1.51), which was somewhat greater than the risk associated with spontaneous terminations (RR, 1.11; 95% CI, 1.02 to 1.20). The association with induced abortions was stronger for those performed before legalization of abortion in 1973 (RR, 1.35; 95% CI, 1.01 to 1.80) than after this time (RR, 1.12; 95% CI, 0.84 to 1.49), suggesting a bias in reporting this sensitive procedure.

Conclusions: A weak positive association was observed between abortion--whether induced or spontaneous--and risk of breast cancer. The increase in risk of breast cancer was somewhat greater among women with a history of induced terminations. However, this association may be due to reporting bias and was not significantly different than the slight risk for spontaneous terminations.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Abortion, Induced / adverse effects
  • Abortion, Induced / statistics & numerical data*
  • Abortion, Spontaneous / complications
  • Abortion, Spontaneous / epidemiology*
  • Adult
  • Aged
  • Bias
  • Breast Neoplasms / epidemiology*
  • Breast Neoplasms / etiology
  • Case-Control Studies
  • Female
  • Humans
  • Logistic Models
  • Middle Aged
  • Pregnancy
  • Registries
  • Risk