Assessing the impact of screening mammography: Breast cancer incidence and mortality rates in Connecticut (1943-2002).

BACKGROUND: Randomized controlled studies demonstrate that early detection and intervention reduce breast cancer mortality by approximately 25%. Though the ultimate goal of screening is to reduce breast cancer deaths, the immediate goal is to detect and treat early-stage tumors before they pose a threat to life.

MATERIALS AND METHODS: To assess the impact of early detection and intervention in the general population, we analyzed breast cancer incidence and mortality rates in the NCI's Historical Connecticut Tumor Registry (1943-2002).

RESULTS: Though breast cancer rates increased for the entire study period, overall incidence rates rose faster than previously following the initiation of mammography screening in the early 1980s in the United States. Of note, stage-specific incidence rates increased 152% (53.2-133.9 per 100,000 woman-years) for early-stage tumors and fell 16% (56.1-47.2 per 100,000 woman-years) for late-stage breast cancers. Period- and cohort-age-specific incidence rates rose dramatically for early-stage tumors among women targeted for screening (ages 40-80 years), whereas rates for regional and distant stages declined modestly among women ages >50 years. Breast cancer mortality rates fell 31.6%.

CONCLUSIONS: Along with increases in incidence rates for early-stage tumors, rates for late-stage disease and breast cancer mortality declined following widespread screening mammography, consistent with effective early detection and improved treatment over time. However, the disparity between the dramatic rise in early-stage tumors compared to the more modest declines in late-stage disease and mortality suggests that many mammography-derived early-stage lesions may never progress to late-stage cancers and pose a threat to life.