Early Detection and Prevention - Screening Group
Screening for cancer implies testing for early stages of disease before symptoms occur. It involves application of an early detection test to a large number of apparently healthy people to identify those having unrecognised cancer. People with positive screening tests 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, it must incorporate an accurate, easy to apply, simple, inexpensive, culturally acceptable, and safe screening test; the disease screened must be common and should have a detectable preclinical stage and effective treatment available; a large proportion of people at risk should participate in screening, investigations and treatment; the local health service infrastructure should be sufficiently developed to provide the diagnostic, treatment and follow-up services. Screening programmes require an efficient organisation to ensure high coverage (>70%) of target populations and to monitor and evaluate outcomes. Hence, screening programmes require significant 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 undesirable complications of treatment. It is important to minimise side effects and increase benefits of screening by adequate quality assurance of screening tests, diagnosis and treatment.
It is important to evaluate the efficacy of a given screening approach to reduce disease burden, harm and cost, as well as its overall cost-effectiveness, before it is considered for widespread implementation in large population settings. The only justification for a screening programme is early diagnosis that leads to a cost-effective and significant reduction in disease burden. If improved outcomes and cost-effectiveness cannot be demonstrated, the rationale for screening is lost. Screening has been implemented mostly for cancer sites such as uterine cervix, breast, and large bowel in developed countries.