Screening Mammography: Overdiagnosis More Common Than Early Detection

By Andrew M. Kaunitz, MD

Dr. Kaunitz is editor-in-chief of NEJM Journal Watch Women's Health, from which this story was adapted. Full coverage is available to subscribers at the link below.

Screening mammography leads to more overdiagnosis than early detection, according to a long-term analysis in the New England Journal of Medicine.

U.S. investigators analyzed population-based cancer registry data in women aged 40 and older. Data from 1975–1979 (prior to widespread screening) and 2000–2002 (the most recent period for which 10-year follow-up data were available) were compared.

With the advent of widespread screening, incidence of small (<2 cm) in situ and invasive breast tumors increased by 162 cases per 100,000 women, whereas incidence of larger tumors decreased by 30 cases per 100,000. These observations indicate that 132 cases per 100,000 reflect overdiagnosis. The authors estimate that screening was responsible for no more than one third of the reduction in breast cancer mortality, with the balance a function of improved treatment.

Comment: This important study clarifies that overdiagnosis associated with screening mammography reflects a substantially unrecognized concern. For my average-risk patients, I will continue to follow U.S. Preventive Services Task Force guidance (biennial screens beginning at age 50), while being flexible when women prefer to initiate screens earlier or undergo them more often.