Population-Based Breast Cancer Screening With Risk-Based and Universal Mammography Screening Compared With Clinical Breast Examination A Propensity Score Analysis of 1 429 890 Taiwanese Women

IMPORTANCE Different screening strategies for breast cancer are available but have not been researched in quantitative detail. OBJECTIVE To assess the benefits and the harms of risk-based and universal mammography screening in comparison with annual clinical breast examination (CBE). DESIGN Population-based cohort study comparing incidences of stage II+ disease and death from breast cancer across 3 breast cancer screening strategies, with adjustment for a propensity score for participation based on risk factors for breast cancer and comparing the 3 strategies for overdetection between January 1999 and December 2009. Asymptomatic women attending outreach screening in the community or undergoing mammography in hospitals were enrolled in the 3 screening programs. INTERVENTIONS Risk-based biennial mammography, universal biennial mammography, and annual CBE. MAIN OUTCOMES AND MEASURES Detection rates, stage II+ disease incidence, mortality from breast cancer, and overdiagnosis were compared using a time-dependent Cox proportional hazards regression model. RESULTS A total of 1 429 890 asymptomatic women attending outreach screening in the community or undergoing mammography in hospitals were enrolled in the 3 screening programs. Detection rates (prevalent screen and subsequent screens per 1000) were the highest for universal biennial mammography (4.86 and 2.98, respectively), followed by risk-based mammography (2.80 and 2.77, respectively), and lowest for annual CBE (0.97 and 0.70, respectively). Universal biennial mammography screening, compared with annual CBE, was associated with a 41% mortality reduction (risk ratio, 0.59; 95% CI, 0.48-0.73) and a 30% reduction of stage II+ breast cancer (RR, 0.70; 95% CI, 0.66-0.74). Risk-based mammography screening was associated with an 8% reduction of stage II+ breast cancer (RR, 0.92; 95% CI, 0.86-0.99) but was not associated with a statistically significant mortality reduction (risk ratio [ RR], 0.86; 95% CI, 0.73-1.02). Estimates of overdiagnosis were no different from CBE for risk-based screening and 13% higher than CBE for universal mammography. CONCLUSIONS AND RELEVANCE Compared with population-based screening for breast cancer with annual CBE, universal biennial mammography resulted in a substantial reduction in breast cancer deaths, whereas risk-based biennial mammography resulted in only a modest benefit. Compared with annual CBE, risk-based and universal mammography screening did not result in significant overdiagnosis of breast cancer.