Assessing the efficacy of cancer screening.

BACKGROUND Population-based cancer screening has been established for several types of cancer in Australia and internationally. Screening may perform differently in practice from randomised controlled trials, which makes evaluating programs complex. MATERIALS AND METHODS We discuss how to assess the evidence of benefits and harms of cancer screening, including the main biases that can mislead clinicians and policy makers (such as volunteer, lead-time, length-time and overdiagnosis bias). We also discuss ways in which communication of risks can inform or mislead the community. RESULTS The evaluation of cancer screening programs should involve balancing the benefits and harms. When considering the overall worth of an intervention and allocation of scarce health resources, decisions should focus on the net benefits and be informed by systematic reviews. Communication of screening outcomes can be misleading. Many messages highlight the benefits while downplaying the harms, and often use relative risks and 5-year survival to persuade people to screen rather than support informed choice. LESSONS LEARNED An evidence based approach is essential when evaluating and communicating the benefits and harms of cancer screening, to minimise misleading biases and the reliance on intuition.