A Randomized Trial of Aspirin to Prevent Colorectal Adenomas in Patients with Previous Colorectal Cancer

Previous trials evaluating aspirin and other nonsteroidal antiinflammatory drugs for preventing colorectal adenomas have used populations at average risk. This randomized, double-blind, placebo-controlled study, the Colorectal Adenoma Prevention Study, evaluated 325 mg per day of aspirin in patients 30 to 80 years of age who had histologically confirmed colon or rectal cancer but were at low risk of recurrence after curative resection of the primary tumor. Those with more advanced disease were eligible if they had been disease-free for longer than 5 years after resection. Colonoscopy was done as part of the usual follow-up routine. A total of 517 patients, 258 randomized to receive placebo and 259 to aspirin, had at least one colonoscopy after randomization; the median interval to the first examination was 11 months. Fewer aspirin-treated patients developed adenomas; 17% of them had at least one adenoma, compared with 27% for placebo patients. The relative risk of a new adenoma in the aspirin group was 0.65 after adjusting for age, sex, stage of cancer, number of colonoscopies, and time to a first postrandomization colonoscopy. The hazard ratio for a new polyp was 0.64 in the aspirin group. Adenomas were of comparable size in the 2 groups, as were the numbers of patients whose adenomas were at least 1 cm in diameter. No substantial difference in adverse effects was noted. A daily 325-mg dose of aspirin lowers the risk of adenoma in patients followed up after resection of a primary colorectal cancer. Despite this clear protective effect, adenomas did develop in some aspirin-treated patients. Aspirin cannot be recommended as a replacement for surveillance colonoscopy.