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Screening for cancer implies testing for early forms of disease before symptoms occur. It involves application of an early detection test to a large number of apparently healthy people to identify those with a high probability of having clinically unrecognized cancer or precancerous lesions. People who test positive are subsequently investigated with diagnostic tests and those with confirmed disease are offered appropriate treatment and follow-up. The objective of screening is to reduce incidence of and/or death from cancer by detecting early preclinical disease when treatment may be easier and more effective than for advanced cancer diagnosed after the symptoms occur.

For screening to be effective, accurate, easy to apply, simple, inexpensive, culturally acceptable, and safe screening tests are essential; the disease screened must be common and should have a detectable preclinical stage, for which effective treatment should be available; a large proportion of people at risk should participate in screening, investigations and treatment; the local health services infrastructure should be sufficiently developed to provide the diagnostic, treatment and follow-up services. Screening programmes require an efficient organization to ensure high coverage (>70%) of target populations and to monitor and evaluate outcomes. Hence, screening programmes require large human and financial resources. Screening has also its own undesired harmful effects due to false-positive results leading to high-levels of anxiety and unnecessary investigations, false-negative results leading to false reassurance, and in certain instances, undesirable side effects/complications of treatment.

It is important to evaluate the efficacy of a given screening approach to reduce the disease and its overall cost-effectiveness, in addition to assessing the harms if any, before it is considered for widespread implementation in large population settings. The justification for a screening programme is early diagnosis that leads to a cost-effective and measurable reduction in disease burden. If improved outcomes and cost-effectiveness cannot be demonstrated, the rationale for screening is lost. Screening has been implemented mostly in developed countries, for cancer sites such as uterine cervix, breast, and large bowel. Screening for cervical and oral cancer has been introduced in few developing countries, but they have been largely ineffective in reducing mortality.


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Examples of major studies are given below:
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