Do the results of the process indicators in the Norwegian Breast Cancer Screening Program predict future mortality reduction from breast cancer?

Continuous emphases of quality control are required to achieve reduction in mortality from breast cancer as a consequence of breast cancer screening. Results of the process indicators in the first 6 years in 4 counties in the Norwegian Breast Cancer Screening Program are evaluated and will be presented. Data from women who had their initial (n = 173402) and subsequent (n = 220 058) screening provide the basis for the analysis. The breast cancer detection ratio was 3.2 the expected incidence (based on the incidence before the screening started, 1991-1995) among the initially screened women, decreasing to 2.3 among the subsequently screened. The ratio of interval cancer among the initially screened was 0.25 and 0.72 of the expected incidence, 0-12 and 13-23 months after screening, respectively. For those subsequently screened the proportions were 0.22 and 0.64, respectively. More than 50% of the invasive tumors were less than 15 mm in size, and more than 75% were lymph node negative, among both the initially and subsequently screened. The process indicators achieved in the NBCSP are promising as regards future mortality reduction. The incidence of interval cancer 13-24 months after screening is higher than recommended in the European guidelines.