Purpose To compare the performance of digital breast tomosynthesis (DBT) and two-dimensional synthetic mammography (SM) with that of digital mammography (DM) in a population-based mammographic screening program. Materials and Methods In this prospective cohort study, data from 37 185 women screened with DBT and SM and from 61 742 women screened with DM as part of a population-based screening program in 2014 and 2015 were included. Early performance measures, including recall rate due to abnormal mammographic findings, rate of screen-detected breast cancer, positive predictive value of recall, positive predictive value of needle biopsy, histopathologic type, tumor size, tumor grade, lymph node involvement, hormonal status, Ki-67 level, and human epidermal growth factor receptor 2 status were compared in women who underwent DBT and SM screening and in those who underwent DM screening by using χ tests, two-sample unpaired t tests, and tests of proportions. Results Recall rates were 3.4% for DBT and SM screening and 3.3% for DM screening (P = .563). DBT and SM screening showed a significantly higher rate of screen-detected cancer compared with DM screening (9.4 vs 6.1 cancers per 1000 patients screened, respectively; P < .001). The rate of detection of tumors 10 mm or smaller was 3.2 per 1000 patients screened with DBT and SM and 1.8 per 1000 patients screened with DM (P < .001), and the rate of grade 1 tumors was 3.3 per 1000 patients screened with DBT and SM versus 1.4 per 1000 patients screened with DM (P < .001). On the basis of immunohistochemical analyses, rates of lymph node involvement and tumor subtypes did not differ between women who underwent DBT and SM screening and those who underwent DM screening. Conclusion DBT and SM screening increased the detection rate of histologically favorable tumors compared with that attained with DM screening. RSNA, 2018 Online supplemental material is available for this article.

B reast cancer is the most common type of cancer among women worldwide, with almost 2.1 million new cases in 2018, and early detection with mammographic screening is considered beneficial to reduce mortality from this disease (1,2). Studies using a paired design have demonstrated a higher rate of screen-detected breast cancer when using standard two-dimensional (2D) digital mammography (DM) in combination with digital breast tomosynthesis (DBT) versus DM alone (3,4), and a randomized controlled trial from Italy reported a 90% increase in breast cancer detection when using DM and DBT together versus DM alone (5).However, the radiation dose of DBT and DM is nearly double that of DM. Thus, radiation concerns make this technique less suitable for population-based screening. Reconstruction algorithms creating 2D synthetic mammograms (SMs) from DBT image volume have become available, making the radiation dose acceptable for . A higher rate of screen-detected breast cancer also has been observed for DBT and SM when compared with DM in nonrandomized studies (9-12), while a randomized controlled trial from Norway reported no statistical difference in detection rate for

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Objective To perform a radiological review of mammograms from prior screening and diagnosis of screen-detected breast cancer in BreastScreen Norway, a population-based screening program. Methods We performed a consensus-based informed review of mammograms from prior screening and diagnosis for screen-detected breast cancers. Mammographic density and findings on screening and diagnostic mammograms were classified according to the Breast Imaging-Reporting and Data System®. Cases were classified based on visible findings on prior screening mammograms as true (no findings), missed (obvious findings), minimal signs (minor/non-specific findings), or occult (no findings at diagnosis). Histopathologic tumor characteristics were extracted from the Cancer Registry of Norway. The Bonferroni correction was used to adjust for multiple testing; p < 0.001 was considered statistically significant. Results The study included mammograms for 1225 women with screen-detected breast cancer. Mean age was 62 years ± 5 (SD); 46% (567/1225) were classified as true, 22% (266/1225) as missed, and 32% (392/1225) as minimal signs. No difference in mammographic density was observed between the classification categories. At diagnosis, 59% (336/567) of true and 70% (185/266) of missed cancers were classified as masses (p = 0.004). The percentage of histological grade 3 cancers was higher for true (30% (138/469)) than for missed (14% (33/234)) cancers (p < 0.001). Estrogen receptor positivity was observed in 86% (387/469) of true and 95% (215/234) of missed (p < 0.001) cancers. Conclusions We classified 22% of the screen-detected cancers as missed based on a review of prior screening mammograms with diagnostic images available. One main goal of the study was quality improvement of radiologists’ performance and the program. Visible findings on prior screening mammograms were not necessarily indicative of screening failure. Key Points • After a consensus-based informed review, 46% of screen-detected breast cancers were classified as true, 22% as missed, and 32% as minimal signs. • Less favorable prognostic and predictive tumor characteristics were observed in true screen-detected breast cancer compared with missed. • The most frequent mammographic finding for all classification categories at the time of diagnosis was mass, while the most frequent mammographic finding on prior screening mammograms was a mass for missed cancers and asymmetry for minimal signs.