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

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.

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