RESUMO
BACKGROUND: After the introduction of a mammography screening program, the incidence of late-stage breast cancer is expected to decrease. The objective of the current study was to evaluate variations in the total incidence of breast cancer and in the incidence of breast cancers with a pathologic tumor (pT) classification of pT2 through pT4 after the introduction of mammography screening in 6 Italian administrative regions. METHODS: The study area included 700 municipalities, with a total population of 692,824 women ages 55 to 74 years, that were targeted by organized mammography screening between 1991 and 2005. The year screening started at the municipal level (year 1) was identified. The years of screening were numbered from 1 to 8. The ratio of the observed 2-year, age-standardized (Europe) incidence rate to the expected rate (the incidence rate ratio [IRR]) was calculated. Expected rates were estimated assuming that the incidence of breast cancer was stable and was equivalent to that in the last 3 years before year 1. RESULTS: The study was based on a total of 14,447 incident breast cancers, including 4036 pT2 through pT4 breast cancers. The total IRR was 1.35 (95% confidence interval, 1.03-1.41) in years 1 and 2, 1.16 (95% confidence interval, 1.10-1.21) in years 3 and 4, 1.14 (95% confidence interval, 1.08-1.20) in years 5 and 6, and 1.14 (95% confidence interval, 1.08-1.21) in years 7 and 8. The IRR for pT2 through pT4 breast cancers was 0.97 (95% confidence interval, 0.90-1.04) in years 1 and 2, 0.81 (95% confidence interval, 0.75-0.88) in years 3 and 4, 0.79 (95% confidence interval, 0.73-0.87) in years 5 and 6, and 0.71 (95% confidence interval, 0.64-0.79) in years 7 and 8. CONCLUSIONS: A significant and stable decrease in the incidence of late-stage breast cancer was observed from the third year of screening onward, when the IRR varied between 0.81 and 0.71.