Outcome of breast cancer screening in Denmark

Abstract

Background: In Denmark, national roll-out of a population-based, screening mammography program took place in 2007-2010. We report on outcome of the first four biennial invitation rounds.

Methods: Data on screening outcome were retrieved from the 2015 and 2016 national screening quality reports. We calculated coverage by examination; participation after invitation; detection-, interval cancer- and false-positive rates; cancer characteristics; sensitivity and specificity, for Denmark and for the five regions.

Results: At the national level coverage by examination remained at 75-77%; lower in the Capital Region than in the rest of Denmrk. Detection rate was slightly below 1% at first screen, 0.6% at subsequent screens, and one region had some fluctuation over time. Ductal carcinoma in situ (DCIS) constituted 13-14% of screen-detected cancers. In subsequent rounds, 80% of screen-detected invasive cancers were node negative and 40% ≤10 mm. False-positive rate was around 2%; higher for North Denmark Region than for the rest of Denmark. Three out of 10 breast cancers in screened women were diagnosed as interval cancers.

Conclusions: High coverage by examination and low interval cancer rate are required for screening to decrease breast cancer mortality. Two pioneer local screening programs starting in the 1990s were followed by a decrease in breast cancer mortality of 22-25%. Coverage by examination and interval cancer rate of the national program were on the favorable side of values from the pioneer programs. It appears that the implementation of a national screening program in Denmark has been successful, though regional variations need further evaluation to assure optimization of the program.

Keywords: Breast cancer; Ductal carcinoma in situ.; Mammography.; Screening..

Fig. 1

Coverage in screening mammography in Denmark 2008–2015 by invitation round and region. Percent and 95% confidence intervals. Notes: 1 South Denmark omitted in 1st round because only 70% of target population was invited. 2 Zealand omitted in 2nd round because the round was stopped before time to synchronize time periods across regions

Fig. 2

Detection rate in screening mammography in Denmark 2008–2015 by region and invitation round. Percent and 95% confidence intervals

Fig. 3

Sensitivity versus 1-specificity in screening mammography in Denmark 2015 by region and invitation round

Fig. 4

Coverage by examination, interval cancers rate and false positive rate in the first four invitation rounds of the pilot screening programs in Copenhagen and Funen and in the Danish national program. Percent and 95% confidence interval.