The impact of the BreastScreen NSW transition from film to digital mammography, 2002-2016: a linked population health data analysis.

OBJECTIVES

To assess the impact of the transition from film to digital mammography in the Australian national breast cancer screening program.

STUDY

DESIGN

Retrospective linked population health data analysis (New South Wales Central Cancer Registry, BreastScreen NSW); interrupted time series analysis.

SETTING

New South Wales, 2002-2016.

PARTICIPANTS

Women aged 40 years or older with breast cancer diagnosed during 2002-2017 who had been screened by BreastScreen NSW and for whom complete follow-up information until the end of the recommended re-screening interval was available.

INTERVENTION: Transition from film to digital mammography; 2009 defined as transition year (digital mammography becomes dominant screening modality).

MAIN OUTCOME MEASURES: Population rates of screen-detected cancer, interval cancer, recalls, and false positive findings.

RESULTS

The study cohort comprised 967 573 women; of the 2 741 555 screens, 1 535 184 used film mammography (2002-2010) and 1 206 371 used digital mammography (2006-2016). The screen-detected cancer rate was 4.86 (95% confidence interval [CI], 4.75-4.97) cases per 1000 screens with film mammography and 6.11 (95% CI, 5.97-6.24) cases per 1000 screens with digital mammography (unadjusted difference, 1.24 [95% CI, 1.06-1.41] cases per 1000 screens). The interval cancer rate was 2.56 (95% CI, 2.48-2.64) cases per 1000 screens with film mammography and 2.84 (95% CI, 2.75-2.94) cases per 1000 screens with digital mammography (unadjusted difference, 0.27 [95% CI, 0.15-0.40] cases per 1000 screens). With the transition to digital mammography, the screen-detected cancer rate increased by 0.07 per 1000 screens, the sum of the decline in the invasive cancer rate (-0.21 cases per 1000 screens) and the rise in the ductal carcinoma in situ detection rate (0.28 cases per 1000 screens); during 2009-2015, it increased by 0.18 cases per 1000 screens per year. With the transition to digital mammography, the interval cancer rate increased by 0.75 cases per 1000 screens (invasive cancer: by 0.69 cases per 1000 screens); during 2009-2015, it declined by 0.13 cases per 1000 screens per year. The recall rate increased by 8.02 per 1000 screens and the false positive rate by 7.16 per 1000 screens following the transition; both rates subsequently declined to pre-transition levels.

CONCLUSIONS

The increased screen-detected cancer rate following the transition to digital mammography was not accompanied by a reduction in interval cancer detection rates.