Colorectal carcinoma: causes, diagnosis, and prevention.

Colorectal carcinoma is the second leading cause of cancer death in the U.S. The risk for colon carcinoma increases after the age of 40 years. Because there is a very significant familial incidence of colorectal carcinoma, this is a major group of individuals who should be screened. The vast majority of colorectal carcinomas are associated with adenomatous polyps of the large intestine. Colonoscopy is the best procedure available to evaluate those at risk; the double-contrast barium enema and flexible sigmoidoscopy also play a significant role in diagnosis. Screening for occult blood in the stool is presently the best tool to evaluate groups for potential colorectal lesions. Although there are still significant problems with occult blood testing, it can account for a definite decrease in morbidity and mortality from colorectal carcinoma.