Maturitas 55 (2006) 103–115 Prior hormone therapy and breast cancer risk in the Women’s Health Initiative randomized trial of estrogen plus progestin Garnet L. Anderson a,* , Rowan T. Chlebowski b , Jacques E. Rossouw c , Rebecca J. Rodabough a , Anne McTiernan a , Karen L. Margolis d , Anita Aggerwal e , J. David Curb f , Susan L. Hendrix g , F. Allan Hubbell h , Jamardan Khandekar i , Dorothy S. Lane j , Norman Lasser k , Ana Maria Lopez l , JoNell Potter m , Cheryl Ritenbaugh l a WHI Clinical Coordinating Center, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, M3-A410, P.O. Box 19024, Seattle, WA 98109-1024, United States b Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center (LABioMed), Torrance, CA, United States c NHLBI-WHI, Rockville, MD, United States d Berman Center for Clinical Research, Hennepin County Medical Center, Minneapolis, MN, United States e Washington Hospital Center, Washington, DC, United States f Department of Geriatric Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI, United States g Department of Obstetrics and Gynecology, Wayne State University School of Medicine/Hutzel Women’s Hospital, Detroit, MI, United States h Department of Medicine, University of California, Irvine, CA, United States i Department of Medicine, Northwestern University, Evanston, IL, United States j State University of New York at Stony Brook, NY, United States k University of Medicine and Dentistry of New Jersey, Newark, NJ, United States l University of Arizona, Tucson, AZ, United States m University of Miami, Miami, FL, United States Received 23 November 2005; received in revised form 28 April 2006; accepted 5 May 2006 Abstract Objectives: To assess the extent to which prior hormone therapy modifies the breast cancer risk found with estrogen plus progestin (E + P) in the Women’s Health Initiative (WHI) randomized trial. Methods: Subgroup analyses of prior hormone use on invasive breast cancer incidence in 16,608 postmenopausal women in the WHI randomized trial of E + P over an average 5.6 years of follow-up. Results: Small but statistically significant differences were found between prior HT users and non-users for most breast cancer risk factors but Gail risk scores were similar. Duration of E + P use within the trial (mean 4.4 years, S.D. 2.0) did not vary by prior * Corresponding author. Tel.: +1 206 667 4699; fax: +1 206 667 4142. E-mail address: garnet@whi.org (G.L. Anderson). 0378-5122/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.maturitas.2006.05.004