Women who continue breast cancer screening after age 70 face a considerable risk for overdiagnosis.
Overdiagnosis — the risk of detecting and treating cancers that would never have caused issues in a person’s lifetime — is increasingly recognized as a harm of breast cancer screening; however, the scope of the problem among older women remains uncertain.
To get an idea, investigators linked Medicare claims data with Surveillance, Epidemiology, and End Results (SEER) data for 54,635 women 70 years or older to compare the incidence of breast cancer and breast cancer-specific death among women who continued screening mammography with those who did not.
The women all had undergone recent screening mammograms and had no history of breast cancer at study entry. Those who had a subsequent mammogram within 3 years were classified as undergoing continued screening while those who did not were classified as not undergoing continued screening.
Overdiagnosis was defined as the difference in cumulative incidence of breast cancer between screened and unscreened women divided by the cumulative incidence among screened women.
Results were adjusted for potential confounders, including age, race, and ethnicity.
Over 80% of women 70-84 years old and more than 60% of women 85 years or older continued screening.
Among women 70-74 years old, the adjusted cumulative incidence of breast cancer was 6.1 cases per 100 screened women vs 4.2 cases per 100 unscreened women; for women aged 75-84 years old, the cumulative incidence was 4.9 per 100 screened women vs 2.6 per 100 unscreened women, and for women 85 years and older, the cumulative incidence was 2.8 vs 1.3 per 100, respectively.
Estimates of overdiagnosis ranged from 31% of breast cancer cases among screened women in the 70-74 age group to 54% of cases in the 85 and older group.
The researchers found no statistically significant reduction in breast cancer-specific death associated with screening in any age or life-expectancy group. Overdiagnosis appeared to be driven by in situ and localized invasive breast cancer, not advanced breast cancer.
The proportion of older women who continue to receive screening mammograms and may experience breast cancer overdiagnosis is “considerable” and “increases with advancing age and with decreasing life expectancy,” the authors conclude. Given potential benefits and harms of screening in this population, “patient preferences, including risk tolerance, comfort with uncertainty, and willingness to undergo treatment, are important for informing screening decisions.”
The study was led by Ilana Richman, MD, MHS, of the Yale School of Medicine, New Haven, Connecticut, and published August 8 in the Annals of Internal Medicine.
The definition of screening mammography in the study may have misclassified some diagnostic mammograms as screening. Using a more conservative definition of screening mammogram, which largely accounted for this misclassification, estimates for overdiagnosis were smaller, ranging from 15% of cases in the 70-74 age group to 44% of cases in the 85 and older group. Results could not be adjusted for breast density, family history, and other breast cancer risk factors not captured by the data.
The work was funded by the National Cancer Institute. One author reported funding from Genentech and Johnson & Johnson.
M. Alexander Otto is a physician assistant with a master’s degree in medical science and a journalism degree from Newhouse. He is an award-winning medical journalist who worked for several major news outlets before joining Medscape. Alex is also an MIT Knight Science Journalism fellow. Email: [email protected] .
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