Originally published as JCO Early Release 10.1200/JCO.2007.14.3081 on February 4 2008

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Oral Contraceptives, Postmenopausal Hormones, and Risk of Asynchronous Bilateral Breast Cancer: The WECARE Study Group

Jane C. Figueiredo, Leslie Bernstein, Marinela Capanu, Kathleen E. Malone, Charles F. Lynch, Hoda Anton-Culver, Marilyn Stovall, Lisbeth Bertelsen, Robert W. Haile, Jonine L. Bernstein

From the Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA; Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, NY; Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA; Department of Epidemiology, University of Iowa, Iowa City, IA; Epidemiology Division, Department of Medicine, University of California, Irvine, CA; Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX; and the Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark

Corresponding author: Leslie Bernstein, PhD, City of Hope Comprehensive Cancer Center, 1500 East Durate Rd, Bldg 173, Durate, CA 91010; e-mail: Ibernstein{at}coh.org

Purpose: To investigate whether oral contraceptive (OC) use and postmenopausal hormones (PMH) are associated with an increased risk of developing asynchronous bilateral breast cancer among women diagnosed with breast cancer younger than 55 years.

Patients and Methods: The WECARE (Women's Environment, Cancer, and Radiation Epidemiology) study is a population-based, multicenter, case-control study of 708 women with asynchronous bilateral breast cancer and 1,395 women with unilateral breast cancer. Risk factor information collected during a telephone interview focused on exposures before and after the first breast cancer diagnosis. Treatment and tumor characteristics were abstracted from medical records. Multivariable conditional logistic regression was used to estimate rate ratios (RR) and 95% CIs.

Results: OC use before the first breast cancer diagnosis was not associated with risk of asynchronous bilateral breast cancer (RR = 0.88; 95% CI, 0.67 to 1.16). OC use after breast cancer diagnosis was also not significantly associated with risk (RR = 1.56; 95% CI, 0.71 to 3.45). Risk did not increase with longer duration of use or among women who had begun using OCs at a younger age. No evidence of an increased risk of asynchronous bilateral breast cancer was observed with PMH use before (RR = 1.21; 95% CI, 0.90 to 1.61) or after breast cancer diagnosis (RR = 1.10; 95% CI, 0.67 to 1.77). Neither duration nor type of PMH were associated with risk. Age at and time since first breast cancer diagnosis did not substantially affect these results.

Conclusion: This study provides no strong evidence that OC or PMH use increases the risk of a second cancer in the contralateral breast.

published online ahead of print at www.jco.org on February 4, 2008.

Supported by National Institutes of Health Grants No. U01-CA83178, R01-CA97397, and R01-CA42949; and a post-PhD Research Fellowship from the National Cancer Institute of Canada (#017602; J.C.F.).

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.