Awareness of the substantial morbidity and mortality attributable to colorectal cancer has focused attention on early detection and prevention through screening and on other strategies such as chemoprevention. Among several agents under evaluation, aspirin appears to have the inside track. Could aspirin reduce the burden of disease associated with the second-leading cause of cancer-related death in the United States?A protective effect of aspirin is biologically plausible. Aspirin works in part through the inhibition of cyclooxygenase-2, an enzyme that is found in colorectal cancer tissue. Epidemiologic studies have shown a consistent 40 to 50 percent reduction in the risk of . . .