SEATTLE-Regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) and aspirin(Drug information on aspirin) lowers the relative risk of colorectal cancer by an overall rate of 24%, according to a study presented at the 67th Annual Scientific Meeting of the American College of Gastroenterology (abstract 12). The rate rises to 32% when aspirin/ NSAIDs are used for more than 2 years. "We have known for years that regular use of NSAIDs lowers the risk of colorectal cancer anywhere from 30% to 50%," said Jia-Qing Huang, MD, research associate, Division of Gastroenterology, McMaster University, Hamilton, Ontario, Canada. Richard H. Hunt, MD, professor of medicine, was senior author of the study. While combined evidence from epidemiological, clinical, and animal studies has shown that NSAIDs are effective in reducing the risk of developing colorectal cancer, long-term use and the magnitude of effect remained unevaluated, Dr. Huang noted. The researchers performed a systematic search of the literature up to March 2002. They found eight casecontrol studies and five cohort studies that met the predefined eligibility criteria. The case-control studies involved 13 study arms, with nearly 12,000 patients and more than 43,000 controls. Statistical combination of these studies showed greater overall aspirin/ NSAIDs use among controls (26%) than among colorectal cancer patients (14.4%). With an odds ratio of 0.76 and a 95% confidence interval of 0.67 to 0.86, the analysis shows a clear protective effect, Dr. Huang said. In a subanalysis, the investigators found that the magnitude of the protective effect was equal for both NSAIDs and aspirin. In the five cohort studies, the incidence of colorectal cancer was 5 per 10,000 person-years among NSAID users vs 5.3 per 10,000 person-years in controls, showing a relative risk of 0.81 (95% CI: 0.72 to 0.92). Subjects using NSAIDs on a regular basis for longer than 2 years had significantly more protection, compared with those using them for less time. "Two years or longer of continuous regular use is required before realization of any chemoprevention effect on colorectal cancer," Dr. Huang said. He noted that their study had several limitations, namely that the extent of NSAID exposure-which included dosage, dose frequency, and treatment duration-varied considerably among the studies. Control populations also varied, and statistical adjustment was not possible for these variations.