284 Colorectal Cancer Despite Colonoscopy: Critical Is the Endoscopist, Not the Withdrawal Time

Background: Aspirin reduces risk of colorectal neoplasia in randomized trials and epidemiological studies and inhibits tumor growth and metastases in animal models. However, the influence of aspirin on survival after diagnosis of colorectal cancer is unknown. Methods: Among 1288 participants diagnosed with Stage I, II, or III colorectal cancer enrolled in two cohorts, we used Cox proportional hazards models to prospectively compare the effect of aspirin use before and after colorectal diagnosis on mortality. Results: Compared to nonusers, participants who regularly used aspirin after colorectal cancer diagnosis experienced a multivariate hazard ratio (HR) for colorectal cancer-specific mortality of 0.72 (95% CI, 0.54-0.97) and overall mortality of 0.82 (95% CI, 0.67-1.00). Among 719 participants who did not use aspirin before diagnosis of colorectal cancer, aspirin use initiated after diagnosis was associated with a multivariate HR for colorectal cancer-specific mortality of 0.55 (95% CI, 0.34-0.89). Among 459 participants with colorectal cancers that were accessible for immunohistochemical assessment, the effect of aspirin differed significantly according to COX-2 expression (Pheterogeneity=0.04). Regular aspirin use after diagnosis was associated with a lower risk of colorectal-cancer specific mortality among those whose primary tumors overexpressed COX-2 (multivariate HR 0.39; 95% CI, 0.20-0.76) whereas aspirin use had no influence on those with primary tumor with weak or absent expression (multivariate HR 1.25; 95% CI, 0.37-4.22). Conclusions: Regular aspirin use after the diagnosis of colorectal cancer may reduce the risk of colorectal cancer-specific mortality, especially among individuals with tumors that overexpress COX-2.