REDUCED RISK OF LARGE-BOWEL ADENOMAS AMONG ASPIRIN USERS

Background: Epidemiological studies have indicated that aspirin consum ption can lower the risk of large-bowel cancer. These studies are not entirely consistent, however, and their interpretation has been compli cated by the possibility that cancer symptoms may have led patients to avoid aspirin or that aspirin may have influenced cancer diagnosis an d treatment. Purpose: Our purpose was to determine the effect of aspir in on risk of large-bowel neoplasms in a study in which aspirin use wo uld not be expected to affect tumor detection and tumor-related sympto ms would not likely influence aspirin use. A less complicated assessme nt of the relationship between aspirin and large-bowel tumors should t hus be possible. Methods: We studied 793 patients enrolled in a clinic al trial of nutrient supplements to prevent large-bowel adenomas. Unli ke invasive cancers, adenomas usually do not cause symptoms or detecta ble gastrointestinal bleeding; thus, adenomas are unlikely to influenc e aspirin use. Each patient had at least one large-bowel adenoma diagn osed and removed shortly before study entry and had been judged to be free of further tumors by colonoscopy. Use of aspirin was assessed by responses on questionnaires administered 6 and 12 months after enrollm ent. We performed complete colonoscopies on all patients 1 year after they entered the study and removed all polyps. Results: Patients who r eported taking aspirin on both questionnaires (consistent users) had a lower risk of new adenomas at their 1-year follow-up colonoscopy (odd s ratio = 0.52; 95% confidence interval = 0.31-0.89) compared with pat ients who did not report using aspirin on either of the questionnaires . The apparent protective effect of consistent aspirin use was present among both men and women and did not appear to be influenced by the n umber of prior adenomas. Conclusions: These data further support the h ypothesis that aspirin has an anti-neoplastic effect in the large bowe l. Nevertheless, the question of whether aspirin should be used to pre vent large-bowel tumors would be best answered by a randomized control led clinical trial specifically designed to address this issue.