Estimation of Overdiagnosis in Breast Cancer Screening

I. Summary The benefit of breast cancer (BC) screening with mammography has been demonstrated by randomized controlled trials (RCTs). However, there is a growing concern about the harms of screening, in particular the problem of overdiagnosis. It occurs when screening detects a breast cancer that would not have presented clinically in the woman's lifetime in the absence of screening. Overdiagnosis results in unnecessary biopsies, surgery and overtreatment with psycho-social consequences. Therefore accurately quantifying the frequency of overdiagnosis is important for informed decision making and policy development. Unfortunately, at diagnosis of an asymptomatic breast cancer it is impossible to determine if the breast cancer will become clinically apparent during the women’s’ lifetime. Thus measurement of the frequency of overdiagnosis is not straightforward.