Large Study Adds to Concerns About Breast Cancer Overdiagnosis with Mammography

By Kelly Young

Edited by David G. Fairchild, MD, MPH

Patients may ask about a new study showing that more mammography screening is associated with a higher rate of breast cancer diagnosis — but not reduced breast cancer mortality. The findings appear in JAMA Internal Medicine.

Researchers used county-level data from national cancer registries to identify 53,000 women aged 40 and older who were diagnosed with breast cancer in the year 2000. An increase in county-wide screening of 10 percentage points was associated with a mean increase of 16% in breast cancer incidence, or an absolute difference of 35–49 cases per 100,000. The increase in incidence was largely limited to cancers 2 cm and smaller. However, higher screening rates were not associated with lower 10-year breast cancer mortality.

The authors write: "The simplest explanation is widespread overdiagnosis, which increases the incidence of small cancer without changing mortality, and therefore matches every feature of the observed data."

Commentators conclude: "In the end, we all need to become comfortable with informing women that we do not know the actual magnitude of overdiagnosis with precision. Part of informed decision making is providing all the information, even our uncertainty."