Efforts in cancer diagnosis: national task forces--large bowel cancer.

Current information from the National Large Bowel Cancer Project and other sources is given concerning new leads and avenues of research that may be used in early diagnosis or possibly in monitoring therapy. The search for biological markers has developed in two general directions: (1) to identify by genetic studies patients with a high probability of developing cancer who will provide insight into biochemical changes as premalignant lesions develop into frankly developed cancer, and (2) to fine differences between tissue and body fluid constituents in normal subjects and patients with cancer. Screening for colon cancer is discussed with a selective diagnostic approach and with emphasis on this approach in early diagnosis of asymptomatic high risk patients.