Introduction to cancer screening: balancing benefits with potential harms

Abstract Cancer is one of the major causes of mortality and morbidity. In Western Europe, one person in three will develop cancer in their lifetime. Cancer screening is important in early detection and intervention for various types of cancer, including breast, cervical and colon cancers. The purpose of cancer screening is to detect pre-cancer or early-stage cancer in individuals. The aim is either to reduce cancer incidence by identifying and treating its precursors or to reduce mortality and morbidity by early detection and early treatment. A screening program is a recurrent process. It starts by identifying the people who are eligible for screening, referred to as the target population. The screening pathway includes a test, further diagnostics and treatment which are specific to each cancer site. The pathway operates as a cycle, with people who have a normal screening test being invited back in a sojourn time-related time frame to be screened again. Screening is effective if all parts of screening pathway are provided with high quality. Therefore, individual data must be collected and evaluated regularly throughout the pathway. The main benefit of screening is early detection to reduce the incidence and mortality of cancer. Other benefits include less aggressive treatments that can improve quality of life. However, screening participants may be exposed to harms of screening without benefiting from it. The most important harm is overdiagnosis, the detection of cancer that would never exist without screening. Overtreatment may occur alongside overdiagnosis. Other harms of screening include false positive and false negative tests. All harms are related to adverse psychological effects, unnecessary investigations, and increased costs. Policymakers need to make sure that screening is effective in reducing mortality and morbidity and that these benefits outweigh the harms. The costs of the program should be affordable within available resources.