Nation-wide data on screening performance during the transition to digital mammography: observations in 6 million screens

Abstract

Purpose: To critically evaluate and confirm previous results regarding the diagnostic accuracy of digital mammography screening (DM), compared to screen-film mammography (SFM) in the whole Dutch screening programme, in the period of 2004-2010, during which a full transition from SFM to DM was made.

Materials and methods: 1.5 million DM and 4.6 million SFM were read in the Dutch national breast cancer screening programme in the period of 2004-2010. We evaluated recall rate, detection rate, positive predictive value and tumour-size distribution for younger and older women, for first time participants and women having a timely subsequent screen. We compared DM screens read by radiologists reading DM and SFM (DM-group) to SFM screens read by these radiologists (SFM-group) and to SFM screens read by radiologists reading only SFM (SFMonly-group).

Results: Recall rate was 2.0% (95% confidence interval (C.I.): 2.0; 2.1) in the DM-group, compared to 1.6% (95% C.I.: 1.6; 1.6) in the SFM-group and 1.6% (95% C.I.: 1.5; 1.6) in the SFM only-group. The overall detection rates were 5.9/1000 screens (95% C.I.: 5.7; 6.0) in the DM-group, 5.1/1000 screens (95% C.I.: 5.0; 5.2) in the SFM-group and 5.0/1000 screens (95% C.I.: 5.0; 5.1) in the SFM only-group. Detection rate rose most markedly in younger women (age 49-54) from 4.0/1000 screens to 5.1/1000 screens (p-value<0.001). Positive predictive value (PPV) in DM rose from 18.4% (95% C.I.: 14.6; 23.1) in 2004 to 32.5% (95% C.I.: 31.7; 33.2) in 2010. Detection rate rose in SFM-group from 5.0/1000 screens (95% C.I.: 4.7; 5.3) in 2004 to 5.5/1000 screens (95% C.I.: 5.2; 5.7) in 2010. Detection rate in DM-group rose mostly due to ductal carcinoma in situ (DCIS) detection especially in younger women/first screens. The proportion of T1a tumours was significantly higher in DM-group; otherwise size distribution did not change significantly for invasive carcinoma. Recall rates were variable between different screening regions.

Conclusion: In accordance to previous, smaller, studies, we can confirm that DM has a higher detection rate compared to SFM, at the cost of a higher recall rate and lower PPV. More DCIS and a higher fraction of very small tumours were detected with DM, which has positive consequences for the stage shift as a result of mass screening.

Keywords: Breast cancer; Detection rate; Digital mammography; Mass screening; Positive predictive value; Recall rate.