Effect of implementing digital breast tomosynthesis (DBT) instead of mammography on population screening outcomes including interval cancer rates: Results of the Trento DBT pilot evaluation

BACKGROUND/AIM: The Trento screening program transitioned to digital breast tomosynthesis (DBT) screening based on evidence that DBT improves breast cancer (BC) detection compared to mammography; an evaluation of the transition to DBT is reported in this pilot study. METHODS: Prospective implementation of DBT screening included women aged ≥50 years who attended the Trento program for biennial screening. DBT screening included DBT acquisitions with synthesized 2D-images. A historical cohort of women who attended the program (January 2013–October 2014) and received digital mammography (DM) provided a comparison group. Independent double-reading (with a third arbitrating read for discordance) was used for DBT and DM screening. Screening outcomes included cancer detection rate (CDR/1000 screens), percentage of screens recalled to assessment (recall%), interval cancer rate (ICR/1000 screens) at 2-year follow-up, and screening sensitivity. Rate ratios (RR) and 95% confidence interval (95%CI) examined outcomes for DBT versus DM screening. RESULTS: From women aged 50–69 years who accepted an invitation to screening (October 2014–October 2016) 46,343 comprised the DBT-screened group: amongst these 402 BCs (includes 50 ductal carcinoma in-situ (DCIS)) were detected (CDR 8.67/1000), whereas 205 BCs (includes 33 DCIS) were detected amongst 37,436 DM screens (CDR 5.48/1000) [RR for CDR:1.58 (1.34–1.87)]. Recall% was lower for DBT (2.55%) than DM (3.21%) [RR:0.79 (0.73–0.86)]. Compared to DM, DBT screening increased CDR for stage I-II BC, for all tumour size and grade categories, and for node-negative BC, but did not increase CDR for DCIS. Estimated ICR for DBT was 1.1/1000 whereas ICR for DM was 1.36/1000 [RR:0.81 (0.55–1.19)]. Screening sensitivity was 88.74% for DBT versus 80.08% for DM [RR:1.11 (0.94–1.31)]. CONCLUSION: DBT significantly improved early-detection measures but did not significantly reduce ICR (relative to DM screening), suggesting that it could add benefit as well as adding over-detection in population BC screening.