The Use of Aspirin for Primary Prevention of Colorectal Cancer: A Systematic Review Prepared for the U.S. Preventive Services Task Force

6 March 2007 | Volume 146 Issue 5 | Pages 365-375

Background: Aspirin for prevention of colorectal cancer is controversial.

Purpose: To examine the benefits and harms of aspirin chemoprevention.

Data Sources: MEDLINE, 1966 to December 2006; EMBASE, 1980 to April 2005; CENTRAL, Cochrane Collaboration's registry of clinical trials; Cochrane Database of Systematic Reviews.

Study Selection: Two independent reviewers conducted multilevel screening to identify randomized, controlled trials (RCTs), case–control studies, and cohort studies of aspirin chemoprophylaxis. For harms, systematic reviews were sought.

Data Extraction: In duplicate, data were abstracted and checked and quality was assessed.

Data Synthesis: Regular use of aspirin reduced the incidence of colonic adenomas in RCTs (relative risk [RR], 0.82 [95% CI, 0.7 to 0.95]), case–control studies (RR, 0.87 [CI, 0.77 to 0.98]), and cohort studies (RR, 0.72 [CI, 0.61 to 0.85]). In cohort studies, regular use of aspirin was associated with RR reductions of 22% for incidence of colorectal cancer. Two RCTs of low-dose aspirin failed to show a protective effect. Data for colorectal cancer mortality were limited. Benefits from chemoprevention were more evident when aspirin was used at a high dose and for periods longer than 10 years. Aspirin use was associated with a dose-related increase in incidence of gastrointestinal complications.

Limitations: Important clinical and methodological heterogeneity in the definitions of regular use, dose, and duration of use of aspirin necessitated careful grouping for analysis.

Conclusions: Aspirin appears to be effective at reducing the incidence of colonic adenoma and colorectal cancer, especially if used in high doses for more than 10 years. However, the possible harms of such a practice require careful consideration. Further evaluation of the cost-effectiveness of chemoprevention compared with, and in combination with, a screening strategy is required.

Author and Article Information

From the University of Calgary, Calgary, Alberta, Canada, and Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, and Carleton University, Ottawa, Ontario, Canada.

Acknowledgments: The authors thank Mary White, ScD, Chief Epidemiology and Applied Research Branch, Centers for Disease Control and Prevention; Patrik Johansson, MD, Medical Officer (AHRQ); Therese Miller, DrPH, Task Order Officer (AHRQ); Janelle Guirguis-Blake, MD, U.S. Preventive Services Task Force (USPSTF) Program Director; and Elizabeth A. Edgerton, MD, MPH, Director of Clinical Prevention, for their contributions. Members of the USPSTF who served as leads for this project include Ned Calonge, MD, MPH; Michael LeFevre, MD, MSPH; Carol Loveland-Cherry, PhD, RN; and Al Siu, MD, MSPH. The authors thank Nav Saloojee, MD, for helping select relevant reports, Tiffany Richards for assisting with the evidence tables, Raymond Daniel for retrieving the full reports, and Chantelle Garritty for helping coordinate the process. The authors also thank Isabella Steffensen and Christine Murray, who dedicated many long hours in the editing of the report and the appendices.

Grant Support: The Evidence Synthesis upon which this article was based was funded by the Centers for Disease Control and Prevention for the Agency for Healthcare Research and Quality and the U.S. Preventive Services Task Force.

Potential Financial Conflicts of Interest: Consultancies: A. Rostom (Novartis); Honoraria: A Rostom (Novartis); Grants received: C. Dubé (Agency for Healthcare Research and Quality/U.S. Preventive Services Task Force), A. Rostom (Agency for Healthcare Research and Quality/U.S. Preventive Services Task Force).

Requests for Single Reprints: Alaa Rostom, MD, MSc (Epi), Division of Gastroenterology, University of Calgary Medical Clinic, 3330 Hospital Drive NW, #G176, Calgary, Alberta, T2N 4N1, Canada; e-mail, arostom{at}ucalgary.ca.

Current Author Addresses: Drs. Dubé and Rostom: Division of Gastroenterology, University of Calgary Medical Clinic, 3330 Hospital Drive NW, #G176, Calgary, Alberta, Canada T2N 1N4.

Drs. Lewin, Tsertsvadze, Barrowman, Sampson, and Moher: Chalmers Research Group, CHEO Research Institute, 401 Smyth Road, Ottawa, Ontario, Canada K1H 8L1.

Dr. Code: Division of Internal Medicine, The Ottawa Hospital–Civic Site, 1053 Carling Avenue, Ottawa, Ontario, Canada K1Y 4E9.

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