Absence of an effect of injectable and implantable progestin-only contraceptives on subsequent risk of breast cancer

Brian L. Strom, Jesse A. Berlin, Anita L. Weber, Sandra A. Norman, Leslie Bernstein, Ronald T. Burkman, Janet R. Daling, Dennis Deapen, Suzanne G. Folger, Kathleen E. Malone, Polly A. Marchbanks, Michael S. Simon, Giske Ursin, Linda K. Weiss, Robert Spirtas

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Abstract

Animal data indicate that both estrogens and progestins could be carcinogenic and that progestins could serve as tumor promoters. Human studies have not confir/B an increased risk of breast cancer from long-term use of oral contraceptives, but have shown an increased risk from hormone replacement therapy including progestins. The present study analyzed the relationship between breast cancer and use of injectable and implantable progestin-only contraceptives. Analyses were perfor/B on data collected in a population-based, multicenter, case-control study, the Women's Contraceptive and Reproductive Experiences Study of the National Institute of Child Health and Human Development. The study involved 4575 randomly sampled cases with invasive breast cancer diagnosed between 1994 and 1998, and 4682 controls, identified using random digit dialing. We assessed the association between exposure to injectable contraceptives and risk of breast cancer. The use of injectable contraceptives was not associated with an increased risk of breast cancer [odds ratio (OR) = 0.9, 95% confidence interval (CI): 0.7, 1.2]. Risk was not increased among current users, defined as women who used injectable contraceptives within 1 year of the reference date (OR = 0.7, 95% CI: 0.4, 1.3) or those who initiated use in the 5 years im/Biately preceding the reference date (OR = 0.9, 95% CI: 0.5, 1.4), or with use beginning before age 35 (OR = 0.9, 95% CI: 0.6, 1.3). Among users, risk increased with increasing duration of use (p = 0.03). However, short-term users (<6 months duration) were at decreased risk relative to never users (OR = 0.6, 95% CI: 0.4, 1.0). When the short-term users were then excluded from the duration-response analysis, the slope of the duration-response became slightly (and nonsignificantly) negative. Risk was not increased among women with 24 or more months of use relative to never users (OR = 1.4, 95% CI: 0.8, 2.5). No increased risk was seen from implantable contraceptives either, although the sample sizes were small. This study does not support an increased risk of breast cancer associated with the use of injectable or implantable progestin-only contraceptives in women aged 35 to 64.

Original languageEnglish (US)
Pages (from-to)353-360
Number of pages8
JournalContraception
Volume69
Issue number5
DOIs
StatePublished - May 1 2004

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All Science Journal Classification (ASJC) codes

  • Reproductive Medicine
  • Obstetrics and Gynecology

Keywords

  • /Broxyprogesterone acetate
  • Breast cancer
  • Contraceptive patch
  • Contraceptives
  • Implantable contraceptives
  • Injectable contraceptives
  • Progestin

Cite this

Strom, B. L., Berlin, J. A., Weber, A. L., Norman, S. A., Bernstein, L., Burkman, R. T., Daling, J. R., Deapen, D., Folger, S. G., Malone, K. E., Marchbanks, P. A., Simon, M. S., Ursin, G., Weiss, L. K., & Spirtas, R. (2004). Absence of an effect of injectable and implantable progestin-only contraceptives on subsequent risk of breast cancer. Contraception, 69(5), 353-360. https://doi.org/10.1016/j.contraception.2003.12.015