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Aspirin Use and Colorectal Cancer: Post-Trial Follow-up Data from the Physicians' Health Study

Til Sturmer, MD, MPH; Robert J. Glynn, ScD, PhD; I-Min Lee, MBBS, ScD; JoAnn E. Manson, MD, DrPH; Julie E. Buring, ScD; and Charles H. Hennekens, MD, DrPH
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From Brigham and Women's Hospital, Harvard Medical School, and Harvard School of Public Health, Boston, Massachusetts; and University of Ulm, Ulm, Germany. Acknowledgments: The authors thank the study participants for their collaboration and the BASF Corp. and Bristol-Meyers Products for logistic support. They also thank the staff of the Physicians' Health Study, particularly Vadim Bubes, Fran LaMotte, Sally Skinner, and Martin Van Denburgh. Grant Support: In part by research grants CA-34944, CA-40360, HL-26490, and HL-34595 from the National Institutes of Health; grant D/96/17743 from the German Academic Exchange Service (Dr. Sturmer); and grant 823B-33287 from the Swiss National Science Foundation (Dr. Sturmer). Requests for Reprints: Charles H. Hennekens, MD, DrPH, Division of Preventive Medicine, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, 900 Commonwealth Avenue East, Boston, MA 02215. Current Author Addresses: Dr. Sturmer: University of Ulm, Department of Epidemiology, Albert-Einstein-Allee 43, D-89081 Ulm, Germany.

Copyright ©2004 by the American College of Physicians

Ann Intern Med. 1998;128(9):713-720. doi:10.7326/0003-4819-128-9-199805010-00003
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Background: In contrast to most observational studies, the randomized Physicians' Health Study found no association between aspirin use and colorectal cancer after 5 years.

Objective: To determine the effect of randomly assigned aspirin treatment and self-selected aspirin use on the incidence of colorectal cancer after 12 years and to identify factors influencing the self-selection of regular aspirin use.

Design: Randomized clinical trial and prospective cohort study.

Setting: Male physicians throughout the United States.

Patients: 22 071 healthy male physicians who were 40 to 84 years of age in 1982.

Intervention: 325 mg of aspirin every other day. In 1988, the aspirin arm of the randomized trial was stopped early. Participants then chose to receive either aspirin or placebo for the rest of the study.

Measurements: Annual questionnaires asking about aspirin use and other variables, including occurrence of cancer.

Results: Colorectal cancer was diagnosed in 341 patients during the study period. Over 12 years of follow-up, random assignment to aspirin was associated with a relative risk for colorectal cancer of 1.03 (95% CI, 0.83 to 1.28). Various gastrointestinal symptoms and diagnoses were strong predictors of less frequent aspirin use in 1988. The relative risk for colorectal cancer in persons who used aspirin frequently after 1988 was 1.07 (CI, 0.75 to 1.53).

Conclusions: In the Physicians' Health Study, both randomized and observational analyses indicate that there is no association between the use of aspirin and the incidence of colorectal cancer. The low dose of aspirin used and the short treatment period may account for the null findings. However, other characteristics associated with the use of aspirin in observational studies remain a plausible alternative explanation.


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Figure 1.
Design of study of aspirin use and colorectal cancer: post-trial follow-up data from the Physicians' Health Study.
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Figure 2.
Relative risk for colorectal cancer in the aspirin group compared with the placebo group.

Bars represent 95% CIs.

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