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Majority of overdiagnosed lesions would spontaneously regress in the absence of screening
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Data from a large study in Norway and Sweden indicate that most breast tumors will never threaten a patient’s survival and will instead undergo spontaneous regression before becoming clinical disease.
Per-Henrik Zahl, MD, PhD, senior statistician with the Norwegian Institute of Public Health in Oslo, argued that mammography screening is associated with 50% overdiagnosis and most of these tumors could spontaneously regress.
“Our analysis of breast cancer incidence in Norway and Sweden indicate that the majority of overdiagnosed lesions would undergo spontaneous regression in the absence of mammography screening,” he said.
Zahl, and his colleague Jan Mæhlen, MD, PhD, with Oslo University Hospital-Ullevál, collected breast cancer incidence rates from 328,927 women in seven Swedish counties. The women were screened biennially from 1980 to 2007.
Zahl and Mæhlen compared those women against the results of a six-year study of incidence of invasive breast cancer they conducted among 317,404 age-matched Norwegian women. Results of that study were published last year in Archives of Internal Medicine. Those women were screened every two years from 1996 to 2001.
They observed 16% more cancers among the women screened three times. Zahl said that observation held across all five five-year age cohorts from 40 to 69, with the largest increase (20%) coming among women aged 40 to 54.
For more information:
- Zahl P. #126. Presented at 2009 Breast Cancer Symposium; October 8-10, 2009, San Francisco
Overdiagnosis does occur in breast cancer screening programs — credible estimates estimate 3% to 9%, not 50%. Failure to apply appropriate methodology leads to overestimating over-diagnosis and, frankly, there are not credible data to suggest a large volume of these tumors spontaneously regress.
– Robert A. Smith, PhD
Director of Cancer Screening, American Cancer Society
Where the rubber hits the road on this one is when you look at it from the personalized cancer therapy perspective. If a patient is diagnosed with a breast cancer, how does she know she has disease that might go away or never affect her? Until such time as we can answer that question, this is an interesting population-based finding, but it’s not actionable information.
– W. Fraser Symmans, MD
Professor of Pathology, Breast Cytopathology and Pharmacogenomics, the University of Texas M.D. Anderson Cancer Center