Perspectives on the Overdiagnosis of Breast Cancer Associated with Mammographic Screening.

Overdiagnosis of breast cancer refers to the screen detection and diagnosis of breast cancer that would not have progressed to symptomatic cancer during a woman's lifetime. Screening mammography, like all screening tests, will result in some overdiagnosis that is attributable to competing causes of death occurring during the lead time (the time period between asymptomatic screen detection and clinical detection) and detection of very indolent cancer. The primary harm of overdiagnosis relates to subsequent (unnecessary) treatment. Importantly, overdiagnosis concerns must be balanced with the lifesaving and morbidity benefits of screening mammography and the prevention of some invasive cancer by detection and treatment of ductal carcinoma in situ. Reasonable estimates of overdiagnosis of women aged 40-80 years are in the order of 1%-10%, with lower values when overdiagnosis is restricted to invasive cancer and among younger women. Prospective identification of an overdiagnosed invasive cancer is not currently possible. Delaying screening until age 50 years or screening biennially rather than annually will not substantially reduce the amount of overdiagnosis of invasive cancer. The clinical significance of overdiagnosis will continue to be minimized as advances in personalized medicine further reduce treatment-associated morbidity.