Colorectal cancer. Risk factors and screening strategies.

Colorectal cancer is common in the United States and frequently discovered too late for cure. Epidemiologic studies suggest a complex relationship between animal fat intake, fecal flora, and risk of development of colorectal cancer, but the actual mechanism of carcinogenesis is still unknown. Early detection might increase the proportion of patients who could be cured of the disease. Screening of asymptomatic subjects over the age of 40 years for fecal occult blood seems to detect cancers before they become invasive. Efforts are needed to ensure that all subjects with positive tests for occult blood are completely examined. We prefer colonoscopy as a single test in that it is both diagnostic and curative early in the disease. The cost-effectiveness of mass screening and its ability to reduce colorectal cancer mortality in our society require further prospective study.