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.

Homologous Recombination Deficiency Across Subtypes of Primary Breast Cancer

PURPOSE

Homologous recombination deficiency (HRD) is highly prevalent in triple-negative breast cancer (TNBC) and associated with response to PARP inhibition (PARPi). Here, we studied the prevalence of HRD in non-TNBC to assess the potential for PARPi in a wider group of patients with breast cancer.

METHODS

HRD status was established using targeted gene panel sequencing (360 genes) and BRCA1 methylation analysis of pretreatment biopsies from 201 patients with primary breast cancer in the phase II PETREMAC trial (ClinicalTrials.gov identifier: NCT02624973). HRD was defined as mutations in BRCA1, BRCA2, BRIP1, BARD1, or PALB2 and/or promoter methylation of BRCA1 (strict definition; HRD-S). In secondary analyses, a wider definition (HRD-W) was used, examining mutations in 20 additional genes. Furthermore, tumor BRCAness (multiplex ligation-dependent probe amplification), PAM50 subtyping, RAD51 nuclear foci to test functional HRD, tumor-infiltrating lymphocyte (TIL), and PD-L1 analyses were performed.

RESULTS

HRD-S was present in 5% of non-TNBC cases (n = 9 of 169), contrasting 47% of the TNBC tumors (n = 15 of 32). HRD-W was observed in 23% of non-TNBC (n = 39 of 169) and 59% of TNBC cases (n = 19 of 32). Of 58 non-TNBC and 30 TNBC biopsies examined for RAD51 foci, 4 of 4 (100%) non-TNBC and 13 of 14 (93%) TNBC cases classified as HRD-S had RAD51 low scores. In contrast, 4 of 17 (24%) non-TNBC and 15 of 19 (79%) TNBC biopsies classified as HRD-W exhibited RAD51 low scores. Of nine non-TNBC tumors with HRD-S status, only one had a basal-like PAM50 signature. There was a high concordance between HRD-S and either BRCAness, high TIL density, or high PD-L1 expression (each P < .001).

CONCLUSION

The prevalence of HRD in non-TNBC suggests that therapy targeting HRD should be evaluated in a wider breast cancer patient population. Strict HRD criteria should be implemented to increase diagnostic precision with respect to functional HRD.

Abstract P6-10-04: Homologous recombination deficiency across subtypes of primary breast cancer

Background: Homologous recombination deficiency (HRD) is highly prevalent in triple-negative breast cancer (TNBC) and predictive of response to PARP inhibition in the primary setting (Eikesdal et al, Ann Oncol, 2021). However, the prevalence of HRD across breast cancer subtypes has not been established. Methods: Pretreatment tumor biopsies from 201 patients (32 TNBC and 169 non-TNBC) with primary breast cancer in the phase II PETREMAC trial (ClinicalTrials #NCT02624973) were examined. These samples underwent targeted cancer gene panel sequencing and BRCA1 promoter methylation analysis to assess HRD status defined by homologous recombination repair (HRR) gene mutations and/or BRCA1 promoter methylation. HRR genes included BRCA1, BRCA2, BRIP1, BARD1, and PALB2 by strict definition (HRR-S), and additionally ABL1, ATM, ATR, ATRX, BLM, CDK12, CHEK1, EMSY, ERCC4, FANCA, FANCC, FANCD2, FANCE, FANCF, FANCG, MEN1, MRE11, NBN, PTEN, and SETD2 by wider definition (HRR-W). HRD strict (HRD-S) was defined as biallelic gene inactivation by HRR-S mutations or BRCA1 methylation. Finally, tumors underwent PAM50 gene expression subtyping and evaluation of functional HRD by RAD51 nuclear foci analysis, for which a low score has been associated with HRD. Results: HRD-S was present in 13% of the breast cancers (total: n= 27/201; TNBC: 15/32; 47%; non-TNBC: 12/169; 7%), whereas HRD-W (HRR-W or BRCA1 methylation) was observed in 29% (total: n=58/201; TNBC: 19/32; 59%; non-TNBC: 39/169; 23%). Among 190 tumors analyzed for PAM50 intrinsic subtype, HRD-S was detected in 3/60 and 4/48 (5% and 8%) of tumors classified as luminal A and B, respectively, 1/35 (3%) of HER2-enriched, 4/21 (19%) of normal-like, and 12/26 (46%) of basal-like tumors. Out of 58 non-TNBC biopsies examined by RAD51 staining, four (7%) were classified as HRD-S and all these were scored as RAD51 low. The remaining 54 non-TNBC samples were homologous recombination proficient, and none of these exhibited functional HRD by RAD51 low scores. All four HRD-S/RAD51 low tumors were hormone receptor-positive, HER2 negative, and belonged to the luminal A (n=1), luminal B (n=2), and basal-like (n=1) subtypes, with HRD caused by germline BRCA1 (gBRCA1), gBRCA2, somatic BRCA1 mutations and BRCA1 methylation, respectively. Conclusion: The prevalence of HRD across all breast cancer subtypes suggests that HRD analysis and therapy targeting such DNA repair defects should be tested in future clinical trials.

Citation Format: Christina Engebrethsen, Synnøve Yndestad, Andrea Herencia-Ropero, Oleksii Nikolaienko, Olav Karsten Vintermyr, Reidun K. Lillestøl, Laura Minsaas, Beryl Leirvaag, Gjertrud Iversen, Bjørnar Gilje, Egil Blix, Helge Espelid, Steinar Lundgren, Jürgen Geisler, Liv Jorunn Vassbotn, Hildegunn S. Aase, Turid Aas, Alba Llop-Guevara, Violeta Serra, Per Eystein Lønning, Stian Knappskog, Hans Petter Eikesdal. Homologous recombination deficiency across subtypes of primary breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-04.

Interval and Subsequent Round Breast Cancer in a Randomized Controlled Trial Comparing Digital Breast Tomosynthesis and Digital Mammography Screening

Background Prevalent digital breast tomosynthesis (DBT) has shown higher cancer detection rates and lower recall rates compared with those of digital mammography (DM). However, data are limited on rates and histopathologic tumor characteristics of interval and subsequent round screen-detected cancers for DBT. Purpose To follow women randomized to screening with DBT or DM and to investigate rates and tumor characteristics of interval and subsequent round screen-detected cancers. Materials and Methods To-Be is a randomized controlled trial comparing the outcome of DBT and DM in organized breast cancer screening. The trial included 28 749 women, with 22 306 women returning for subsequent DBT screening 2 years later (11 201 and 11 105 originally screened with DBT and DM, respectively). Differences in rates, means, and distribution of histopathologic tumor characteristics between women prevalently screened with DBT versus DM were evaluated with Z tests, t tests, and χ² tests. Relative risk (RR) with 95% CIs was calculated for the cancer rates. Results Interval cancer rates were 1.4 per 1000 screens (20 of 14 380; 95% CI: 0.9, 2.1) for DBT versus 2.0 per 1000 screens (29 of 14 369; 95% CI: 1.4, 2.9; P = .20) for DM. The rates of subsequent round screen-detected cancer were 8.1 per 1000 (95% CI: 6.6, 10.0) for women originally screened with DBT and 9.1 per 1000 (95% CI: 7.4, 11.0; P = .43) for women screened with DM. The distribution of tumor characteristics did not differ between groups for either interval or subsequent screen-detected cancer. The RR of interval cancer was 0.69 (95% CI: 0.39, 1.22; P = .20) for DBT versus DM, whereas RR of subsequent screen-detected cancer for women prevalently screened with DBT versus DM was 0.89 (95% CI: 0.67, 1.19; P = .43). Conclusion Rates of interval or subsequent round screen-detected cancers and their tumor characteristics did not differ between women originally screened with digital breast tomosynthesis (DBT) versus digital mammography. The analysis suggests that the benefits of prevalent DBT screening did not come at the expense of worse downstream screening performance measures in a population-based screening program. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Taourel in this issue.

Mammographic features and screening outcome in a randomized controlled trial comparing digital breast tomosynthesis and digital mammography

PURPOSE

To compare the distribution of mammographic features among women recalled for further assessment after screening with digital breast tomosynthesis (DBT) versus digital mammography (DM), and to assess associations between features and final outcome of the screening, including immunohistochemical subtypes of the tumour.

METHODS

This randomized controlled trial was performed in Bergen, Norway, and included 28,749 women, of which 1015 were recalled due to mammographic findings. Mammographic features were classified according to a modified BI-RADS-scale. The distribution were compared using 95 % confidence intervals (CI).

RESULTS

Asymmetry was the most common feature of all recalls, 24.3 % (108/444) for DBT and 38.9 % (222/571) for DM. Spiculated mass was most common for breast cancer after screening with DBT (36.8 %, 35/95, 95 %CI: 27.2-47.4) while calcifications (23.0 %, 20/87, 95 %CI: 14.6-33.2) was the most frequent after DM. Among women screened with DBT, 0.13 % (95 %CI: 0.08-0.21) had benign outcome after recall due to indistinct mass while the percentage was 0.28 % (95 %CI: 0.20-0.38) for DM. The distributions were 0.70 % (95 %CI: 0.57-0.85) versus 1.46 % (95 %CI: 1.27-1.67) for asymmetry and 0.24 % (95 %CI: 0.16-0.33) versus 0.54 % (95 %CI: 0.43-0.68) for obscured mass, among women screened with DBT versus DM, respectively. Spiculated mass was the most common feature among women diagnosed with non-luminal A-like cancer after DBT and after DM.

CONCLUSIONS

Spiculated mass was the dominant feature for breast cancer among women screened with DBT while calcifications was the most frequent feature for DM. Further studies exploring the clinical relevance of mammographic features visible particularly on DBT are warranted.

Digital breast tomosynthesis in a population based mammographic screening program: Breast compression and early performance measures

PURPOSE

We aimed to determine if compression force or pressure could be associated with early performance measures for women screened with digital breast tomosynthesis (DBT) in BreastScreen Norway. Early performance measures included rates of consensus, recall, and screen-detected breast cancer.

METHOD

Data on compression force and pressure, compressed breast thickness and breast characteristics were extracted from an automated software for density assessment of DBT screening examinations for 25,286 women. For descriptive analyses, force (Newton, N) and pressure (kilopascal, kPa) were categorized into quartiles. Analyses were stratified by mammographic view, craniocaudal (CC) and mediolateral oblique (MLO). Logistic regression with restricted cubic splines was used to investigate the association between force and pressure as continuous exposures and early performance measures adjusted for age, compressed breast thickness and fibroglandular volume.

RESULTS

Mean age of the screened women was 60.7 (SD = 5.2) years. Mean compression force was 90.8 (SD = 14.2) N for CC and 106.3 (SD = 20.6) N for MLO, and pressure was 11.3 (SD = 3.6) kPa for CC and 8.7 (SD = 2.0) kPa for MLO. The highest rates of screen-detected cancer were observed for low force (1.04 % for <82.5 N for CC and 1.07 % for <92.0 N for MLO) and low pressure (1.07 % for <7.2 kPa for MLO). No association was found between force or pressure as continuous exposures and early performance measures in adjusted regression analyses.

CONCLUSIONS

We found the highest rates of screen-detected cancer for low force and pressure, but no significant association between continuous values of force or pressure and early performance measures in DBT. The findings might indicate that the levels of force and pressure in DBT are of lower significance for screening performance than reported in standard digital mammography.

A randomized controlled trial of digital breast tomosynthesis versus digital mammography in population-based screening in Bergen: interim analysis of performance indicators from the To-Be trial

Objectives

To describe a randomized controlled trial (RCT) of digital breast tomosynthesis including synthesized two-dimensional mammograms (DBT) versus digital mammography (DM) in a population-based screening program for breast cancer and to compare selected secondary screening outcomes for the two techniques.

Methods

This RCT, performed in Bergen as part of BreastScreen Norway, was approved by the Regional Committees for Medical Health Research Ethics. All screening attendees in Bergen were invited to participate, of which 89% (14,274/15,976) concented during the first year, and were randomized to DBT (n = 7155) or DM (n = 7119). Secondary screening outcomes were stratified by mammographic density and compared using two-sample t-tests, chi-square tests, ANOVA, negative binomial regression and tests of proportions (z tests).

Results

Mean reading time was 1 min 11 s for DBT and 41 s for DM (p < 0.01). Mean time spent at consensus was 3 min 12 s for DBT and 2 min 12 s for DM (p < 0.01), while the rate of cases discussed at consensus was 6.4% and 7.4%, respectively for DBT and DM (p = 0.03). The recall rate was 3.0% for DBT and 3.6% for DM (p = 0.03). For women with non-dense breasts, recall rate was 2.2% for DBT versus 3.4% for DM (p = 0.04). The rate did not differ for women with dense breasts (3.6% for both). Mean glandular dose per examination was 2.96 mGy for DBT and 2.95 mGy for DM (p = 0.433).

Conclusions

Interim analysis of a screening RCT showed that DBT took longer to read than DM, but had significantly lower recall rate than DM. We found no differences in radiation dose between the two techniques.

Key Points

• In this RCT, DBT was associated with longer interpretation time than DM

• Recall rates were lower for DBT than for DM

• Mean glandular radiation dose did not differ between DBT and DM

Abstract 1201: Breast cancer risk factors and volumetric breast density in a national breast cancer screening program

Background: Studying associations between percent or absolute volumetric breast density (VBD) with age and menopausal status, and whether the associations are modified by demographic, lifestyle, reproductive, or hormonal exposures, can uncover underlying biological mechanisms and improve breast cancer risk prediction.

Material and methods: The cohort consisted of women (aged 49-71 years) who participated in the Norwegian Breast Cancer Screening Program (NBCPS) between 2007 and 2014, had information on VBD and completed questionnaires on standard breast cancer risk factors as part of the program (n=46 428). We estimated least squared means of percent and absolute VBD associated with age at mammography, menopausal status, age at menopause, reproductive and hormonal factors (ages at menarche and first birth, number of pregnancies lasting ≥6 months, duration of breastfeeding, oral contraceptives, and menopausal hormone therapy), self-reported height and body mass index (BMI), education, and lifestyle factors (physical activity, alcohol intake, and smoking).

Results: For a 5-year increase in age, the reduction in percent VBD was -0.18% in pre- and perimenopausal and -0.08% in postmenopausal women, and the reduction in absolute VBD was -0.11 cm³ in pre- and perimenopausal and -0.03 cm³ in postmenopausal women (p for interaction by menopausal status &lt;0.001). In multivariate analyses, the associations between demographic, lifestyle, reproductive and hormonal risk factors and percent and absolute VBD were highly significant, however the magnitude of the effects were modest (1-2%), and the range of percent VBD across levels of risk factors rather narrow. The strongest association was with BMI, which was inversely associated with percent VBD, with a threefold higher percent VBD in women with BMI&lt;20 kg/m² than in women with BMI&gt;33 kg/m² (12.9% versus 3.9%). Interestingly, BMI was positively associated with absolute VBD, with 1.5

times higher VBD in women with BMI≥33 kg/cm² (37.9 cm³ versus 58.4 cm³). Models were adjusted for BMI, education, and parity.

Conclusion: This large cohort analysis found percent and absolute VBD to decrease with increasing age both among pre/perimenopausal and postmenopausal women. The rate of decline was larger among pre/perimenopausal women. Percent and absolute VBD are associated with several established breast cancer risk factors, especially BMI, where the direction of the association differed for percent and absolute VBD.

Citation Format: Kirsti V. Hjerkind, Merete Ellingjord-Dale, Anna L. Johansson, Hildegunn S. Aase, Solveig R. Hoff, Solveig Hofvind, Siri Fagerheim, Linda Vos, Isabel dos Santos Silva, Giske Ursin. Breast cancer risk factors and volumetric breast density in a national breast cancer screening program [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1201.