Performance of an AI System for Breast Cancer Detection on Screening Mammograms from BreastScreen Norway.

"Just Accepted" papers have undergone full peer review and have been accepted for publication in Radiology: Artificial Intelligence. This article will undergo copyediting, layout, and proof review before it is published in its final version. Please note that during production of the final copyedited article, errors may be discovered which could affect the content. Purpose To explore the standalone breast cancer detection performance at different risk score thresholds of a commercially available artificial intelligence (AI) system. Materials and Methods This retrospective study included information from 661,695 digital mammographic examinations performed among 242,629 female individuals screened as a part of x, 2004-2018. The study sample included 3807 screen-detected cancers (SDC) and 1110 interval breast cancers (IC). A continuous examination level risk score by the AI system was used to measure performance as the area under the receiver operating characteristic curve (AUC) with 95% CIs and cancer detection at different AI risk score thresholds. Results The AUC of the AI system was 0.93 (95% CI: 0.92-0.93) for SDC and IC combined and 0.97 (95% CI: 0.97-0.97) for SDC. In a setting where 10% of the examinations with the highest AI risk scores were defined as positive and 90% with the lowest scores as negative, 92.0% (3502/3807) of the SDC and 44.6% (495/1100) of the IC were identified by AI. In this scenario, 68.5% (10 987/16 029) of false positive screening results (negative recall assessment) were considered negative by AI. When 50% was used as the cut-off, 99.3% (3781/3807) of the SDC and 85.2% (946/1100) of the IC were identified as positive by AI, while 17.0% (2725/16 029) of the false positives were considered as negative. Conclusion The AI system showed high performance in detecting breast cancers within 2 years of screening mammography and a potential for triaging low-risk mammograms to reduce radiologist workload. ©RSNA, 2024.

Women's attitudes and perspectives on the use of artificial intelligence in the assessment of screening mammograms.

PURPOSE: To investigate attitudes and perspectives on the use of artificial intelligence (AI) in the assessment of screening mammograms among women invited to BreastScreen Norway. METHOD: An anonymous survey was sent to all women invited to BreastScreen Norway during the study period, October 10, 2022, to December 25, 2022 (n = 84,543). Questions were answered on a 10-point Likert scale and as multiple-choice, addressing knowledge of AI, willingness to participate in AI studies, information needs, confidence in AI results and AI assisted reading strategies, and thoughts on concerns and benefits of AI in mammography screening. Analyses were performed using χ2 and logistic regression tests. RESULTS: General knowledge of AI was reported as extensive by 11.0% of the 8,355 respondents. Respondents were willing to participate in studies using AI either for decision support (64.0%) or triaging (54.9%). Being informed about use of AI-assisted image assessment was considered important, and a reading strategy of AI in combination with one radiologist preferred. Having extensive knowledge of AI was associated with willingness to participate in AI studies (decision support; odds ratio [OR]: 5.1, 95% confidence interval [CI]: 4.1-6.4, and triaging; OR: 3.4, 95% CI: 2.8-4.0) and trust in AI's independent assessment (OR: 6.8, 95% CI: 5.7, 8.3). CONCLUSIONS: Women invited to BreastScreen Norway had a positive attitude towards the use of AI in image assessment, given that human readers are still involved. Targeted information and increased public knowledge of AI could help achieve high participation in AI studies and successful implementation of AI in mammography screening.

Digital breast tomosynthesis in mammographic screening: false negative cancer cases in the To-Be 1 trial.

OBJECTIVES: The randomized controlled trial comparing digital breast tomosynthesis and synthetic 2D mammograms (DBT + SM) versus digital mammography (DM) (the To-Be 1 trial), 2016-2017, did not result in higher cancer detection for DBT + SM. We aimed to determine if negative cases prior to interval and consecutive screen-detected cancers from DBT + SM were due to interpretive error. METHODS: Five external breast radiologists performed the individual blinded review of 239 screening examinations (90 true negative, 39 false positive, 19 prior to interval cancer, and 91 prior to consecutive screen-detected cancer) and the informed consensus review of examinations prior to interval and screen-detected cancers (n = 110). The reviewers marked suspicious findings with a score of 1-5 (probability of malignancy). A case was false negative if ≥ 2 radiologists assigned the cancer site with a score of ≥ 2 in the blinded review and if the case was assigned as false negative by a consensus in the informed review. RESULTS: In the informed review, 5.3% of examinations prior to interval cancer and 18.7% prior to consecutive round screen-detected cancer were considered false negative. In the blinded review, 10.6% of examinations prior to interval cancer and 42.9% prior to consecutive round screen-detected cancer were scored ≥ 2. A score of ≥ 2 was assigned to 47.8% of negative and 89.7% of false positive examinations. CONCLUSIONS: The false negative rates were consistent with those of prior DM reviews, indicating that the lack of higher cancer detection for DBT + SM versus DM in the To-Be 1 trial is complex and not due to interpretive error alone. CRITICAL RELEVANCE STATEMENT: The randomized controlled trial on digital breast tomosynthesis and synthetic 2D mammograms (DBT) and digital mammography (DM), 2016-2017, showed no difference in cancer detection for the two techniques. The rates of false negative screening examinations prior to interval and consecutive screen-detected cancer for DBT were consistent with the rates in prior DM reviews, indicating that the non-superior DBT performance in the trial might not be due to interpretive error alone. KEY POINTS: • Screening with digital breast tomosynthesis (DBT) did not result in a higher breast cancer detection rate compared to screening with digital mammography (DM) in the To-Be 1 trial. • The false negative rates for examinations prior to interval and consecutive screen-detected cancer for DBT were determined in the trial to test if the lack of differences was due to interpretive error. • The false negative rates were consistent with those of prior DM reviews, indicating that the lack of higher cancer detection for DBT versus DM was complex and not due to interpretive error alone.

Long-term follow-up of complex oncoplastic breast-conserving surgery, standard breast conservation and skin-sparing mastectomy in DCIS - a register-based study.

BACKGROUND: Few studies evaluate oncological safety in complex oncoplastic breast-conserving surgery(C-OBCS) for DCIS. It still needs to be defined whether it is equivalent to standard breast conservation(S-BCS) or an alternative to skin-sparing mastectomy(SSM). This study compares local recurrence rates(LR), disease-free survival(DFS) and overall survival (OS) between the three surgical techniques. METHODS: We conducted a retrospective register-based study on LR, DFS and OS of patients operated with S-BCS(n=1388), C-OBCS (n=106) or skin-sparing mastectomy (n=218) for DCIS diagnosed 2007-2020. Data was extracted from the Norwegian Breast Cancer Registry. RESULTS: In the S-BCS, C-OBCS and SSM groups, median age was 60, 58 and 51 years (p<0.001), median size 15, 25, and 40 mm (p<0.001) and median follow-up 55, 48 and 76 months. At ten years, the overall LR was 12.7%, 14.3% for S-BCS, 11.2% for C-OBCS and 6.8% for SSM. Overall DFS at ten years was 82.3%, 80.5% for S-BCS, 82.4% for C-OBCS and 90.4% for SSM. At ten years, the OS was 93.8%, 93.0% in S-BCS, 93.3% in C-OBCS and 96.6% in the SSM group. Weighted Kaplan Meier plots showed that SSM had a significantly higher DFS than S-BCS (p=0.003) and C-OBCS (p=0.029). DFS in C-OBCS versus S-BCS and the difference in OS was not significant (p=0.264). CONCLUSION: SSM had a significantly higher DFS than S-BCS and C-OBCS. The difference in DFS between S-BCS and C-OBCS, and OS between the three groups was not statistically significant. Our study suggests that C-OBCS is a safe alternative to S-BCS and SSM.

Early performance measures following regular versus irregular screening attendance in the population-based screening program for breast cancer in Norway.

OBJECTIVE: Irregular attendance in breast cancer screening has been associated with higher breast cancer mortality compared to regular attendance. Early performance measures of a screening program following regular versus irregular screening attendance have been less studied. We aimed to investigate early performance measures following regular versus irregular screening attendance. METHODS: We used information from 3,302,396 screening examinations from the Cancer Registry of Norway. Examinations were classified as regular or irregular. Regular was defined as an examination 2 years ± 6 months after the prior examination, and irregular examination >2 years and 6 months after prior examination. Performance measures included recall, biopsy, screen-detected and interval cancer, positive predictive values, and histopathological tumor characteristics. RESULTS: Recall rate was 2.4% (72,429/3,070,068) for regular and 3.5% (8217/232,328) for irregular examinations. The biopsy rate was 1.0% (29,197/3,070,068) for regular and 1.7% (3825/232,328) for irregular examinations, while the rate of screen-detected cancers 0.51% (15,664/3,070,068) versus 0.86% (2003/232,328), respectively. The adjusted odds ratio was 1.53 (95% CI: 1.49-1.56) for recall, 1.73 (95% CI: 1.68-1.80) for biopsy, and 1.68 (95% CI: 1.60-1.76) for screen-detected cancer after irregular examinations compared to regular examinations. The proportion of lymph node-positive tumors was 20.1% (2553/12,719) for regular and 25.6% (426/1662) for irregular examinations. CONCLUSION: Irregular attendance was linked to higher rates of recall, needle biopsies, and cancer detection. Cancers detected after irregular examinations had less favorable histopathological tumor characteristics compared to cancers detected after regular examinations. Women should be encouraged to attend screening when invited to avoid delays in diagnosis.

Norwegian radiologists' expectations of artificial intelligence in mammographic screening - A cross-sectional survey.

PURPOSE: To explore Norwegian breast radiologists' expectations of adding artificial intelligence (AI) in the interpretation procedure of screening mammograms. METHODS: All breast radiologists involved in interpretation of screening mammograms in BreastScreen Norway during 2021 and 2022 (n = 98) were invited to take part in this anonymous cross-sectional survey about use of AI in mammographic screening. The questionnaire included background information of the respondents, their expectations, considerations of biases, and ethical and social implications of implementing AI in screen reading. Data was collected digitally and analyzed using descriptive statistics. RESULTS: The response rate was 61% (60/98), and 67% (40/60) of the respondents were women. Sixty percent (36/60) reported ≥10 years' experience in screen reading, while 82% (49/60) reported no or limited experience with AI in health care. Eighty-two percent of the respondents were positive to explore AI in the interpretation procedure in mammographic screening. When used as decision support, 68% (41/60) expected AI to increase the radiologists' sensitivity for cancer detection. As potential challenges, 55% (33/60) reported lack of trust in the AI system and 45% (27/60) reported discrepancy between radiologists and AI systems as possible challenges. The risk of automation bias was considered high among 47% (28/60). Reduced time spent reading mammograms was rated as a potential benefit by 70% (42/60). CONCLUSION: The radiologists reported positive expectations of AI in the interpretation procedure of screening mammograms. Efforts to minimize the risk of automation bias and increase trust in the AI systems are important before and during future implementation of the tool.

Breast cancer missed at screening; hindsight or mistakes?

PURPOSE: To investigate radiologists' interpretation scores of screening mammograms prior to diagnosis of screen-detected and interval breast cancers retrospectively classified as missed or true negative. METHODS: We included data on radiologists' interpretation scores at screening prior to diagnosis for 1223 screen-detected and 1007 interval cancer cases classified as missed or true negative in an informed consensus-based review. All prior screening examinations were independently scored 1-5 by two radiologists; score 1 by both was considered concordant negative, score ≥ 2 by one radiologist discordant, and score ≥ 2 by both concordant positive. We analyzed associations between interpretation, review categories, mammographic features and histopathological findings using descriptive statistics and logistic regression. RESULTS: Among screen-detected cancers, 31% of missed and 10% of true negative cancers had discordant or concordant positive interpretation at prior screening. The corresponding percentages for interval cancer were 21% and 8%. Age-adjusted odds ratio (OR) and 95% confidence interval (CI) for missed screen-detected cancer was 3.8 (95% CI: 2.6-5.4) after discordant and 5.5 (95% CI: 3.2-9.5) after concordant positive interpretation, using concordant negative as reference. Corresponding ORs for missed interval cancer were 3.0 (95% CI: 2.0-4.5) for discordant and 6.3 (95% CI: 2.3-17.5) for concordant positive interpretation. Asymmetry was the dominating mammographic feature at prior screening for all, except concordant positive screen-detected cancers where a mass dominated. Histopathological characteristics did not vary statistically with interpretation. CONCLUSIONS: Most cancers were interpreted negatively at screening prior to diagnosis. Increased risk for missed screen-detected or interval cancer was observed after positive interpretation at prior screening.

Screening outcome for interpretation by the first and second reader in a population-based mammographic screening program with independent double reading.

BACKGROUND: Double reading of screening mammograms is associated with a higher rate of screen-detected cancer than single reading, but different strategies exist regarding reader pairing and blinding. Knowledge about these aspects is important when considering strategies for future use of artificial intelligence in mammographic screening. PURPOSE: To investigate screening outcome, histopathological tumor characteristics, and mammographic features stratified by the first and the second reader in a population based screening program for breast cancer. MATERIAL AND METHODS: The study sample consisted of data from 3,499,048 screening examinations from 834,691 women performed during 1996-2018 in BreastScreen Norway. All examinations were interpreted independently by two radiologists, 272 in total. We analyzed interpretation score, recall, and cancer detection, as well as histopathological tumor characteristics and mammographic features of the cancers, stratified by the first and second readers. RESULTS: For Reader 1, the rate of positive interpretations was 4.8%, recall 2.3%, and cancer detection 0.5%. The corresponding percentages for Reader 2 were 4.9%, 2.5%, and 0.5% (P < 0.05 compared with Reader 1). No statistical difference was observed for histopathological tumor characteristics or mammographic features when stratified by Readers 1 and 2. Recall and cancer detection were statistically higher and histopathological tumor characteristics less favorable for cases detected after concordant positive compared with discordant interpretations. CONCLUSION: Despite reaching statistical significance, mainly due to the large study sample, we consider the differences in interpretation scores, recall, and cancer detection between the first and second readers to be clinically negligible. For practical and clinical purposes, double reading in BreastScreen Norway is independent.

Screen-detected and interval breast cancer after concordant and discordant interpretations in a population based screening program using independent double reading.

OBJECTIVES: To analyze rates, odds ratios (OR), and characteristics of screen-detected and interval cancers after concordant and discordant initial interpretations and consensus in a population-based screening program. METHODS: Data were extracted from the Cancer Registry of Norway for 487,118 women who participated in BreastScreen Norway, 2006-2017, with 2 years of follow-up. All mammograms were independently interpreted by two radiologists, using a score from 1 (negative) to 5 (high suspicion of cancer). A score of 2+ by one of the two radiologists was defined as discordant and 2+ by both radiologists as concordant positive. Consensus was performed on all discordant and concordant positive, with decisions of recall for further assessment or dismiss. OR was estimated with logistic regression with 95% confidence interval (CI), and histopathological tumor characteristics were analyzed for screen-detected and interval cancer. RESULTS: Among screen-detected cancers, 23.0% (697/3024) had discordant scores, while 12.8% (117/911) of the interval cancers were dismissed at index screening. Adjusted OR was 2.4 (95% CI: 1.9-2.9) for interval cancer and 2.8 (95% CI: 2.5-3.2) for subsequent screen-detected cancer for women dismissed at consensus compared to women with concordant negative scores. We found 3.4% (4/117) of the interval cancers diagnosed after being dismissed to be DCIS, compared to 20.3% (12/59) of those with false-positive result after index screening. CONCLUSION: Twenty-three percent of the screen-detected cancers was scored negative by one of the two radiologists. A higher odds of interval and subsequent screen-detected cancer was observed among women dismissed at consensus compared to concordant negative scores. Our findings indicate a benefit of personalized follow-up. KEY POINTS: • In this study of 487,118 women participating in a screening program using independent double reading with consensus, 23% screen-detected cancers were detected by only one of the two radiologists. • The adjusted odds ratio for interval cancer was 2.4 (95% confidence interval: 1.9, 2.9) for cases dismissed at consensus using concordant negative interpretations as the reference. • Interval cancers diagnosed after being dismissed at consensus or after concordant negative scores had clinically less favorable prognostic tumor characteristics compared to those diagnosed after false-positive results.

Patterns of aggressiveness: risk of progression to invasive breast cancer by mammographic features of calcifications in screen-detected ductal carcinoma in situ.

BACKGROUND: Mammographic features of calcifications on mammograms showing invasive breast cancer are associated with survival. Less is known about mammographic features and progression to invasive breast cancer among women treated for ductal carcinoma in situ (DCIS). PURPOSE: To investigate mammographic features of calcifications in screen-detected DCIS in women who later did and did not get diagnosed with invasive breast cancer. MATERIAL AND METHODS: This registry-based nested case-control study analyzed data from women with screen-detected DCIS in BreastScreen Norway, 1995-2016. Within this cohort of women with DCIS, those who were later diagnosed with invasive breast cancer (cases) were matched (1:2) to women who were not diagnosed with invasive breast cancer (controls) after their DCIS and by the end of 2016. Information on mammographic features were collected by a national radiological review, where screening mammograms were reviewed locally at each of the 16 breast centers in Norway. We used conditional logistic regression analysis to estimate associations between mammographic features of calcifications in the DCIS mammogram and the risk of subsequent invasive breast cancer. RESULTS: We found a higher risk of invasive breast cancer associated with fine linear branching (casting) morphology (odds ratio 20.0; 95% confidence interval [CI] 2.5-158.9) compared to fine linear or fine pleomorphic morphology. Regional or diffuse distribution showed an odds ratio of 2.8 (95% CI 1.0-8.2) compared to segmental or linear distribution. CONCLUSION: Mammographic features of calcifications in screen-detected DCIS were of influence on the risk of invasive breast cancer. Unfavorable characteristics of DCIS were fine linear branching morphology, and regional or diffuse distribution.

True and Missed Interval Cancer in Organized Mammographic Screening: A Retrospective Review Study of Diagnostic and Prior Screening Mammograms.

RATIONALE AND OBJECTIVES: To explore radiological aspects of interval breast cancer in a population-based screening program. MATERIALS AND METHODS: We performed a consensus-based informed review of mammograms from diagnosis and prior screening from women diagnosed with interval cancer 2004-2016 in BreastScreen Norway. Cases were classified as true (no findings on prior screening mammograms), occult (no findings at screening or diagnosis), minimal signs (minor/non-specific findings) and missed (obvious findings). We analyzed mammographic findings, density, time since prior screening, and histopathological characteristics between the classification groups. RESULTS: The study included 1010 interval cancer cases. Mean age at diagnosis was 61 years (SD = 6), mean time between screening and diagnosis 14 months (SD = 7). A total of 48% (479/1010) were classified as true or occult, 28% (285/1010) as minimal signs and 24% (246/1010) as missed. We observed no differences in mammographic density between the groups, except from a higher percentage of dense breasts in women with occult cancer. Among cancers classified as missed, about 1/3 were masses and 1/3 asymmetries at prior screening. True interval cancers were diagnosed later in the screening interval than the other classification categories. No differences in histopathological characteristics were observed between true, minimal signs and missed cases. CONCLUSION: In an informed review, 24% of the interval cancers were classified as missed based on visibility and mammographic findings on prior screening mammograms. Three out of four true interval cancers were diagnosed in the second year of the screening interval. We observed no statistical differences in histopathological characteristics between true and missed interval cancers.

Radiological review of prior screening mammograms of screen-detected breast cancer.

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.

Survival among women diagnosed with screen-detected or interval breast cancer classified as true, minimal signs, or missed through an informed radiological review.

OBJECTIVES: "True" breast cancers, defined as not being visible on prior screening mammograms, are expected to be more aggressive than "missed" cancers, which are visible in retrospect. However, the evidence to support this hypothesis is limited. We compared the risk of death from any cause for women with true, minimal signs, and missed invasive screen-detected (SDC) and interval breast cancers (IC). METHODS: This nation-wide study included 1022 SDC and 788 IC diagnosed through BreastScreen Norway during 2005-2016. Cancers were classified as true, minimal signs, or missed by five breast radiologists in a consensus-based informed review of prior screening and diagnostic images. We used multivariable Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of death from any cause associated with true, minimal signs, and missed breast cancers, adjusting for age at diagnosis, histopathologic tumour diameter and grade, and subtype. Separate models were created for SDC and IC. RESULTS: Among SDC, 463 (44%) were classified as true and 242 (23%) as missed; among IC, 325 (39%) were classified as true and 235 (32%) missed. Missed SDC were associated with a similar risk of death as true SDC (HR = 1.20, 95% CI (0.49, 2.46)). Similar results were observed for missed versus true IC (HR = 1.31, 95% CI (0.77, 2.23)). CONCLUSIONS: We did not observe a statistical difference in the risk of death for women diagnosed with true or missed SDC or IC; however, the number of cases reviewed and follow-up time limited the precision of our estimates. KEY POINTS: • An informed radiological review classified screen-detected and interval cancers as true, minimal signs, or missed based on prior screening and diagnostic mammograms. • It has been hypothesised that true cancers, not visible on the prior screening examination, may be more aggressive than missed cancers. • We did not observe a statistical difference in the risk of death from any cause for women with missed versus true screen-detected or interval breast cancers.

Interval and Consecutive Round Breast Cancer after Digital Breast Tomosynthesis and Synthetic 2D Mammography versus Standard 2D Digital Mammography in BreastScreen Norway.

Background Screening that includes digital breast tomosynthesis (DBT) with two-dimensional (2D) synthetic mammography (SM) or standard 2D digital mammography (DM) results in detection of more breast cancers than does screening with DM alone. A decrease in interval breast cancer rates is anticipated but is not reported. Purpose To compare rates and characteristics of (a) interval breast cancer in women screened with DBT and SM versus those screened with DM alone and (b) screen-detected breast cancer at consecutive screenings with DM. Materials and Methods This prospective cohort study from BreastScreen Norway included women screened with DBT and SM (study group) or DM alone (control group) between February 2014 and December 2015 (baseline). All women, except nonattendees, women with breast cancer, and those who exceeded the upper age limit, were consecutively screened with DM after 2 years. Interval breast cancer, sensitivity, and specificity were estimated for women screened at baseline. Recall, screen-detected breast cancer, and positive predictive value were analyzed for consecutively screened women. A χ2 test, t test (P < .001 after Bonferroni correction indicated a significant difference), and binomial regression model were used to analyze differences across groups. Results A total of 92 404 women who underwent baseline screening (mean age, 59 years ± 6 [standard deviation]) were evaluated; 34 641 women in the study group (mean age, 59 years ± 6) were screened with DBT and SM and 57 763 women in the control group (mean age, 59 years ± 6) were screened with DM. A total of 26 474 women in the study group (mean age, 60 years ± 5) and 45 543 women in the control group (mean age, 60 years ± 5) were consecutively screened with DM. Rates of interval breast cancer were 2.0 per 1000 screened women in the study group and 1.5 per 1000 screened women in the control group (P = .12). No differences in histopathologic characteristics of interval breast cancer were observed. In the consecutive screening round, rates of screen-detected breast cancer were 3.9 per 1000 screened women (study group) and 5.6 per 1000 screened women (control group) (P = .001). Rates of histologic grade 1 invasive cancer were 0.5 per 1000 screened women (study group) and 1.3 per 1000 screened women (control group) (P = .001). Conclusion No differences in interval breast cancer rates or tumor characteristics were observed in women screened with DBT and SM compared with women screened with DM. Higher rates of low-grade screen-detected tumors were observed in the control group at consecutive screening. © RSNA, 2019 Online supplemental material is available for this article.

Screening outcome for consecutive examinations with digital breast tomosynthesis versus standard digital mammography in a population-based screening program.

OBJECTIVES: To retrospectively investigate early performance measures of digital breast tomosynthesis (DBT) versus standard digital mammography (DM) for consecutive screening rounds. METHODS: We included information about 35,736 women screened in BreastScreen Norway, 2008-2016, with at least two consecutive screening examinations. The pair of two consecutive screening examinations was the unit of analysis, and results from the subsequent examination were the measure of interest. Screening technique changed during the study period, resulting in four study groups: DM after DM, DBT after DM, DM after DBT, and DBT after DBT. We compared selected early performance measures between the study groups. RESULTS: Recall for DM after DM was 3.6% and lower for all other study groups (p < 0.001). The rate of screen-detected breast cancer was 4.6/1000 for DM after DM; for DBT after DM and DBT after DBT, it was 9.9/1000 and 8.3/1000, respectively (p < 0.001 relative to DM after DM), and for DM after DBT 4.3/1000. The rate of tubular carcinoma was higher for DBT after DBT or after DM compared with DM after DM (p < 0.01). The rate of histologic grade 1 tumors was higher for DBT after DM compared with DM after DM (p < 0.001). We did not observe any statistical difference in the interval cancer rates. CONCLUSIONS: Lower recall and higher cancer detection rates for screening with DBT were sustainable over two consecutive screening rounds. Positive predictive values were higher for DBT than DM. There were no differences in the interval cancer rates between the study groups. KEY POINTS: • There is limited knowledge about early performance measures for screening with digital breast tomosynthesis beyond one screening round. • A decline in recall rate and an incline in the rate of screen-detected breast cancer were observed for women screened with DBT compared with DM, irrespective of prior screening technique. The interval breast cancer rate did not differ statistically for women screened with DBT versus DM. • Tumor characteristics tended to be prognostic favorable for DBT compared with DM with no differences in rates of more advanced cancers. The clinical significance of increased cancer detection and the potential for future mortality reduction remain unknown.

Digital Breast Tomosynthesis and Synthetic 2D Mammography versus Digital Mammography: Evaluation in a Population-based Screening Program.

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 χ2 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.