The cumulative risk of false-positive screening results across screening centres in the Norwegian Breast Cancer Screening Program.

BACKGROUND

Recall for assessment in mammographic screening entails an inevitable number of false-positive screening results. This study aimed to investigate the variation in the cumulative risk of a false positive screening result and the positive predictive value across the screening centres in the Norwegian Breast Cancer Screening Program.

METHODS

We studied 618,636 women aged 50-69 years who underwent 2,090,575 screening exams (1996-2010. Recall rate, positive predictive value, rate of screen-detected cancer, and the cumulative risk of a false positive screening result, without and with invasive procedures across the screening centres were calculated. Generalized linear models were used to estimate the probability of a false positive screening result and to compute the cumulative false-positive risk for up to ten biennial screening examinations.

RESULTS

The cumulative risk of a false-positive screening exam varied from 10.7% (95% CI: 9.4-12.0%) to 41.5% (95% CI: 34.1-48.9%) across screening centres, with a highest to lowest ratio of 3.9 (95% CI: 3.7-4.0). The highest to lowest ratio for the cumulative risk of undergoing an invasive procedure with a benign outcome was 4.3 (95% CI: 4.0-4.6). The positive predictive value of recall varied between 12.0% (95% CI: 11.0-12.9%) and 19.9% (95% CI: 18.3-21.5%), with a highest to lowest ratio of 1.7 (95% CI: 1.5-1.9).

CONCLUSIONS

A substantial variation in the performance measures across the screening centres in the Norwegian Breast Cancer Screening Program was identified, despite of similar administration, procedures, and quality assurance requirements. Differences in the readers' performance is probably of influence for the variability. This results underscore the importance of continuous surveillance of the screening centres and the radiologists in order to sustain and improve the performance and effectiveness of screening programs.