Screening Detects Many Breast Cancers, but How Many Are Overdiagnosed?

Overdiagnosis occurs when a screening test detects a cancer that might have remained clinically undetectable or asymptomatic during a patient's lifetime. To estimate overdiagnosis rates associated with mammography, investigators conducted a meta-analysis of data from several countries and evaluated incidence of breast cancer in screened populations (i.e., after introduction of national or regional screening mammography programs) compared with that in nonscreened populations (i.e., before introduction of such programs).

In the U.K., the estimated overdiagnosis rate for invasive breast cancer in middle-aged women (age range, 50–64) was 41%. Overdiagnosis estimates ranged from 30% to 42% in Manitoba (Canada), New South Wales (Australia), Sweden…