Estimating Breast Cancer Overdiagnosis After Screening Mammography Among Older Women in the United States

Abstract

Background: Overdiagnosis is increasingly recognized as a harm of breast cancer screening, particularly for older women.

Objective: To estimate overdiagnosis associated with breast cancer screening among older women by age.

Design: Retrospective cohort study comparing the cumulative incidence of breast cancer among older women who continued screening in the next interval with those who did not. Analyses used competing risk models, stratified by age.

Setting: Fee-for-service Medicare claims, linked to the SEER (Surveillance, Epidemiology, and End Results) program.

Patients: Women 70 years and older who had been recently screened.

Measurements: Breast cancer diagnoses and breast cancer death for up to 15 years of follow-up.

Results: This study included 54 635 women. Among women aged 70 to 74 years, the adjusted cumulative incidence of breast cancer was 6.1 cases (95% CI, 5.7 to 6.4) per 100 screened women versus 4.2 cases (CI, 3.5 to 5.0) per 100 unscreened women. An estimated 31% of breast cancer among screened women were potentially overdiagnosed. For women aged 75 to 84 years, cumulative incidence was 4.9 (CI, 4.6 to 5.2) per 100 screened women versus 2.6 (CI, 2.2 to 3.0) per 100 unscreened women, with 47% of cases potentially overdiagnosed. For women aged 85 and older, the cumulative incidence was 2.8 (CI, 2.3 to 3.4) among screened women versus 1.3 (CI, 0.9 to 1.9) among those not, with up to 54% overdiagnosis. We did not see statistically significant reductions in breast cancer-specific death associated with screening.

Limitations: This study was designed to estimate overdiagnosis, limiting our ability to draw conclusions on all benefits and harms of screening. Unmeasured differences in risk for breast cancer and differential competing mortality between screened and unscreened women may confound results. Results were sensitive to model specifications and definition of a screening mammogram.

Conclusion: Continued breast cancer screening was associated with greater incidence of breast cancer, suggesting overdiagnosis may be common among older women who are diagnosed with breast cancer after screening. Whether harms of overdiagnosis are balanced by benefits and for whom remains an important question.

Primary funding source: National Cancer Institute.

Figure 1:. Study schematic.

Each horizontal line represents an individual in the study. Study entry begins at the date of the mammogram (triangular arrowhead) or pseudomammogram (x shape), which must be within 3 years of the 2002 mammogram. The time between the 2002 mammogram and study entry are similar for both the screened and unscreened group, and both groups include only women who have survived and are breast cancer free at the time of cohort entry. The solid bars represent the follow up period, which begins at the time of the mammogram or pseudommamogram date and ends either at death or breast cancer diagnosis (diamond) or end of follow up in 2017 (circle).

Figure 2:. Cumulative incidence of breast cancer by screening status and age.

Figure panels depict cumulative incidence of breast cancer (breast cancer cases per 100 women) among women screened or not screened at cohort entry over available follow up. Shaded areas indicate 95% confidence intervals. Panel A: Age 70–74, Panel B: Age 75–84 years, Panel C: Age 85 and older.

Figure 2:. Cumulative incidence of breast cancer by screening status and age.

Figure panels depict cumulative incidence of breast cancer (breast cancer cases per 100 women) among women screened or not screened at cohort entry over available follow up. Shaded areas indicate 95% confidence intervals. Panel A: Age 70–74, Panel B: Age 75–84 years, Panel C: Age 85 and older.

Figure 2:. Cumulative incidence of breast cancer by screening status and age.

Figure panels depict cumulative incidence of breast cancer (breast cancer cases per 100 women) among women screened or not screened at cohort entry over available follow up. Shaded areas indicate 95% confidence intervals. Panel A: Age 70–74, Panel B: Age 75–84 years, Panel C: Age 85 and older.