The value of screening.

While it seems obvious that diagnosis of cancers by screening early in their asymptomatic stages should result in improved outcomes, for most cancers proof in clinical practice is elusive. Various characteristics of cancers themselves, screening tests, and screening programs, are critical in estimating the potential value of particular screening efforts. Cancer favorable for screening are those with a high prevalence in the patients screening (high-risk patients), a long detectable preclinical phase, and conditions in which early treatment beneficially alters the natural history. A good screening test is one with high sensitivity and specificity, as the test is commonly performed and interpreted, and minimal financial and other costs or risks. Favorable evaluation of a screening program includes demonstrated reduction in morbidity and mortality, preferably in a randomized controlled trial. Interpretation of experimental and nonexperimental results of screening programs in complex. Evaluation of the multidimensional costs of screening depends on the value system of the observer: patient, physician, or public health official. Comparison of costs and benefits with those of other activities is helpful in decision making and in assessing the value of screening.