A new study suggests that it can, but the practical implications are unclear.
Can aspirin prevent colorectal cancer? Two large randomized primary prevention trials showed no effect after 10 years of follow-up (Journal Watch May 8 1998 and Aug 2 2005), but perhaps this time frame was too short.
Investigators studied long-term cancer outcomes in two randomized studies from the U.K. In one trial, 5139 men (mean age, 62) received aspirin (300 or 500 mg daily) or no aspirin for 5 to 6 years. In the other, 2449 patients with a recent cerebrovascular event received aspirin (300 or 1200 mg daily) or placebo for 1 to 7 years. Data on cancers and deaths for a median of 23 years after study entry were obtained from national registries. In both trials, patients who took aspirin had significantly fewer colorectal cancers during the second decade of follow-up (hazard ratio, 0.60), but not before. Further analysis showed a significant risk reduction between 10 and 14 years after randomization, but not after.
The authors also reviewed 30 relevant observational studies. In 19 case-control studies, patients with colorectal cancer used significantly less aspirin or nonsteroidal anti-inflammatory drugs than controls (odds ratio, 0.80). In 11 cohort studies, reduced risk for colon cancer was generally associated with higher doses of aspirin or NSAIDs and with use of aspirin or NSAIDs for more than 10 years.
Comment: This study suggests that high-dose aspirin daily for at least 5 years reduces the risk for colon cancer 10 to 14 years later. But an editorialist argues that there are still too many unanswered questions to recommend aspirin for primary prevention.
— Bruce Soloway, MD
Published in Journal Watch General Medicine May 24, 2007
Flossmann E et al. Effect of aspirin on long-term risk of colorectal cancer: Consistent evidence from randomised and observational studies. Lancet 2007 May 12; 369:1603-13.