Reduction in late-stage breast cancer incidence in the mammography era: Implications for overdiagnosis of invasive cancer.

BACKGROUND: Mammographic screening is expected to decrease the incidence of late-stage breast cancer. In the current study, the authors determined the decrease in late-stage cancer incidence and the changes in invasive cancer incidence that occurred in the mammographic era after adjusting for prescreening temporal trends. METHODS: Breast cancer incidence and stage data were obtained from the Surveillance, Epidemiology, and End Results program. The premammography period (1977-1979) was compared with the mammographic screening period (2007-2009) for women aged ≥ 40 years. The authors estimated prescreening temporal trends using 5 measures of annual percentage change (APC). Stage-specific incidence values from 1977 through 1979 (baseline) were adjusted using APC values of 0.5%, 1.0%, 1.3%, and 2.0% and then compared with observed stage-specific incidence in 2007 through 2009. RESULTS: Prescreening APC temporal trend estimates ranged from 0.8% to 2.3%. The joinpoint estimate of 1.3% for women aged ≥ 40 years approximated the 4-decade long APC trend of 1.2% noted in the Connecticut Tumor Registry. At an APC of 1.3%, late-stage breast cancer incidence decreased by 37% (56 cases per 100,000 women) with a reciprocal increase in early-stage rates noted from 1977 through 1979 to 2007 through 2009. Resulting late-stage cancer incidence decreased from 21% at an APC of 0.5% to 48% at an APC of 2.0%. Total invasive breast cancer incidence decreased by 9% (27 cases per 100,000 women) at an APC of 1.3%. CONCLUSIONS: There is evidence that a substantial reduction in late-stage breast cancer has occurred in the mammography era when appropriate adjustments are made for prescreening temporal trends. At background APC estimates of ≥ 1%, the total invasive breast cancer incidence also decreased.