Early Detection and Prevention - Screening Group
Screening involves looking for early signs of a particular disease by applying an early detection test in healthy people who do not have any symptoms. Screening for cancer aims to find cancers at the earliest possible stage, or early tissue or cellular changes, the treatment of which will prevent cancer. Thus, cancer screening aims to prevent cancer or detect it at a very early, curable stage. 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, for which treatment may be easier and more effective than for advanced cancer diagnosed after the symptoms occur.
For screening to be effective, it must incorporate a screening test that is accurate, feasible, simple, affordable, culturally acceptable, and safe; the disease screened for must be common and should be detectable before symptoms occur, and effective treatment should be available for early stages; a large proportion of people at risk should participate in screening, investigations, and treatment; and the local health services should be sufficiently developed to provide the diagnostic, treatment, and follow-up services. Screening programmes require an efficient organization to ensure high participation (>70%) of people targeted for early detection, and to monitor and evaluate the effectiveness of screening in reducing cancer incidence and/or deaths without causing harms. Hence, screening programmes require significant human and financial resources. Screening also has 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 minimize the side-effects and increase the benefits of screening by providing screening tests, diagnosis, and treatment with adequate quality assurance inputs.
It is important to evaluate the efficacy of a new screening method 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 ensured, the rationale for screening is lost. Cancer screening programmes do not exist in many low-income countries and are few in middle-income countries. Screening has been implemented mostly for cancer sites such as the uterine cervix, breast, and large bowel in developed countries. The ultimate goal of the Screening Group′s research initiatives is to catalyse the widespread implementation of feasible and cost-effective screening programmes in low- and middle-income countries.