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Conjugated Equine Estrogens and Colorectal Cancer Incidence and Survival: The Women's Health Initiative Randomized Clinical Trial

¹ University of Arizona College of Medicine, Tucson, Arizona; ² Fred Hutchinson Cancer Research Center, Seattle, Washington; ³ University of Alabama at Birmingham, Birmingham, Alabama; ⁴ University of Pittsburgh, Pittsburgh, Pennsylvania; ⁵ Stanford University, Palo Alto, California; ⁶ University of California, San Diego, California; ⁷ University of California, Irvine, California; ⁸ State University of New York, Stony Brook, New York; ⁹ John H. Stroger Jr. Hospital of Cook County, Chicago, Illinois; ¹⁰ Wayne State University, Detroit, Michigan; ¹¹ Veterans Affairs Medical Center and George Washington University, Washington, DC; and ¹² Los Angeles Biomedical Research Institute, Torrance, California

Requests for reprints: Cheryl Ritenbaugh, Department of Family and Community Medicine, The University of Arizona, 1450 North Cherry Avenue, Tucson, AZ 85719. Phone 520-626-1033; Fax 520-626-6134. E-mail: ritenbau{at}email.arizona.edu

Background: In separate Women's Health Initiative randomized trials, combined hormone therapy with estrogen plus progestin reduced colorectal cancer incidence but estrogen alone in women with hysterectomy did not. We now analyze features of the colorectal cancers that developed and examine the survival of women following colorectal cancer diagnosis in the latter trial.

Participants and Methods: 10,739 postmenopausal women who were 50 to 79 years of age and had undergone hysterectomy were randomized to conjugated equine estrogens (0.625 mg/d) or matching placebo. Colorectal cancer incidence was a component of the monitoring global index of the study but was not a primary study endpoint. Colorectal cancers were verified by central medical record and pathology report review. Bowel exam frequency was not protocol defined, but information on their use was collected.

Results: After a median 7.1 years, there were 58 invasive colorectal cancers in the hormone group and 53 in the placebo group [hazard ratio, 1.12; 95% confidence interval (95% CI), 0.77-1.63]. Tumor size, stage, and grade were comparable in the two randomization groups. Bowel exam frequency was also comparable in the two groups. The cumulative mortality following colorectal cancer diagnosis among women in the conjugated equine estrogen group was 34% compared with 30% in the placebo group (hazard ratio, 1.34; 95% CI, 0.58-3.19).

Conclusions: In contrast to the preponderance of observational studies, conjugated equine estrogens in a randomized clinical trial did not reduce colorectal cancer incidence nor improve survival after diagnosis. (Cancer Epidemiol Biomarkers Prev 2008;17(10):2609–18)

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