Balancing the benefits and detriments among women targeted by the Norwegian Breast Cancer Screening Program.

OBJECTIVE

To compute a ratio between the estimated numbers of lives saved from breast cancer death and the number of women diagnosed with a breast cancer that never would have been diagnosed during the woman's lifetime had she not attended screening (epidemiologic over-diagnosis) in the Norwegian Breast Cancer Screening Program.

METHODS

The Norwegian Breast Cancer Screening Program invites women aged 50-69 to biennial mammographic screening. Results from published studies using individual level data from the programme for estimating breast cancer mortality and epidemiologic over-diagnosis comprised the basis for the ratio. The mortality reduction varied from 36.8% to 43% among screened women, while estimates on epidemiologic over-diagnosis ranged from 7% to 19.6%. We computed the average estimates for both values. The benefit-detriment ratio, number of lives saved, and number of women over-diagnosed were computed for different scenarios of reduction in breast cancer mortality and epidemiologic over-diagnosis.

RESULTS

For every 10,000 biennially screened women, followed until age 79, we estimated that 53-61 (average 57) women were saved from breast cancer death, and 45-126 (average 82) were over-diagnosed. The benefit-detriment ratio using average estimates was 1:1.4, indicating that the programme saved about one life per 1-2 women with epidemiologic over-diagnosis.

CONCLUSION

The benefit-detriment ratio estimates of the Norwegian Breast Cancer Screening Program, expressed as lives saved from breast cancer death and epidemiologic over-diagnosis, should be interpreted with care due to substantial uncertainties in the estimates, and the differences in the scale of values of the events compared.