Abstract
The aim of screening is to identify disease at a premalignant or early stage before symptoms are present on the basis of evidence that detection of preinvasive disease can prevent cancer or that treatment at an earlier stage can improve outcomes. To ensure the principle that screening should do more good than harm, the health and economic outcomes of a new screening test should be evaluated in large clinical trials, together with its sensitivity, specificity and acceptability. In addition to the benefits, there are risks, limitations and challenges associated with screening that need to be considered by health professionals and patients. Chapter 17 sets out to equip the reader to discuss the aims and principles of screening, to explain the key elements of an effective screening test, to discuss the limitations and potential harms of screening and to consider the psychological impact of screening for individuals at high risk of cancer.