Breast cancer screening with digital breast tomosynthesis: Is independent double reading still required?

Purpose: The European guidelines recommend independent double reading in mammography screening programs. The prospective randomized controlled trial TOSYMA tested the superiority of digital breast tomosynthesis and synthetic mammography (DBT+SM) over digital mammography (DM) for invasive breast cancer detection. This sub-analysis compares the true-positive readings of screening-detected breast cancers resulting from independent double readings in the two trial arms. Materials and methods: The 1:1 randomized TOSYMA trial was executed in 17 screening units between 07/2018 and 12/2020. This sub-analysis included 49,762 women in the test arm (DBT+SM) and 49,796 women in the control arm (DM). The true-positive reading results (invasive breast cancers and ductal carcinoma in situ) from 83 readers were determined and merged in a double reading result. Results: DBT+SM screening detected 416 women with breast cancer and DM screening detected 306. Double readings of DBT+SM examinations led to a single true-positive together with a single false-negative result in 26.9 % of cancer cases (112/416), and in 22.2 % of cases (68/306) in the DM examinations. The cancer detection rate with discordant reading results was 2.3 per 1,000 women screened with DBT+SM and 1.4 per 1,000 with DM. Discordant reading results occurred most often for invasive breast cancers [DBT+SM 75.9 % (85/112), DM 67.6 % (46/68)], category T1 [DBT+SM 67.9 % (76/112), DM 55.9 % (38/68)], and category 4a [DBT+SM: 67.6 % (73/112); DM: 84.6 % (55/68)]. Conclusion: The higher breast cancer detection rate with DBT screening includes a relevant percentage of breast cancers that were only detected by one reader in an independent double reading. As in digital mammography, independent double reading continues to be justified in screening with digital breast tomosynthesis.