Colorectal cancer is a leading cause of cancer death in the United States. Mortality remains high because most colorectal cancers are detected after there has been regional or distant spread, precluding curative surgical resection. With this in mind, screening strategies have been recommended for asymptomatic individuals which hope to reduce mortality from colon cancer by detecting and removing premalignant adenomatous polyps or early malignant lesions. Screening of asymptomatic individuals over age 50 with sigmoidoscopy and fecal occult blood tests has been advocated by the American Cancer Society. However, current screening will identify only 50% of patients who have adenomatous polyps. More sensitive tests for polyp detection, like colonoscopy, are costly, require extensive resources and are unlikely to be used for screening large populations. Ideal screening would identify patients with the highest risk of cancer and target more sensitive screening tests at this population. The identification of low cost, easily collectible risk factors which can be used to target patients for the more sensitive screening tests is the primary purpose of this study. Since a major segment of the veteran population is over the age of 50, there will be a substantial impact in reduction of both mortality and morbidity due to colon cancer and attendant cost savings to the VA for treatment if such risk factors can be identified.

Phase I is a cross-sectional study designed to identify risk factors for large (>1 cm) adenomatous polyps. Approximately 3200 asymptomatic subjects (age 50-75) have completed risk factor assessment, medical and dietary histories, and have undergone complete colonoscopy examination. This will identify for comparison purposes a polyp-free control group and is the first large prospective study to include such a group. Data at colonoscopy will characterize the prevalence, size and distribution of adenomatous polyps. This will permit an assessment of sensitivity of sigmoidoscopy in this population. In addition, tissue from normal rectal mucosa will be analyzed for evidence of cell proliferation activity. The primary focus of Phase I is a risk factor analysis. A multivariate analysis will be performed to determine the relationship of historical and environmental factors as well as cell proliferation activity with the presence of adenomatous polyps. A cohort consisting of a subgroup of polyp patients (large and small) and matched polyp-free controls will be tracked longitudinally to determine polyp occurrence/recurrence rates.

Phase II of the study is a long-term follow-up study designed to evaluate the relative risk of two repeat colonoscopies.

Phase III is an extension in follow-up of an additional five years, a total of ten years in all, to include all study patients. The primary focus will be on documenting long-term mortality and medical outcomes as well as occurrence/reoccurrence of neoplasia with special emphasis on ten-year cancer rates.