Prevention and early detection of cancer.

The axiom that prevention is better than cure is especially true for a serious disease such as cancer for which therapy is expensive and seldom fully effective. However, it is only for some cancers that the major determinants are known and for which primary prevention programs are likely to result in substantial reduction in incidence. Past efforts at primary prevention have not been very successful where avoidance of cancer determinants involves changing pleasurable personal habits or has major economic effects. Control of the disease is now largely based on therapy. Because successful therapy is influenced by the stage of the disease at diagnosis there is increasing interest in early detection through the application of various screening techniques. Only some of these have been demonstrably effective in reducing cancer mortality. The introduction of any mass screening program should be based on an assessment of its costs, risks, and effectiveness in reducing mortality from the disease.