Breast Cancer Detection Better with DBT/Synthetic Mammography Combo

November 10, 2020
Whitney J. Palmer
Whitney J. Palmer

Not only did this combination improve breast cancer detection, but it could also catch more potentially invasive cancers earlier.

Breast cancer detection is better when radiologists opt for digital breast tomosynthesis (DBT) with synthetic mammography (SM) rather than digital mammography (DM) alone. In fact, DBT could pick up potentially invasive cancers earlier.

Those are the findings of a new study published Nov. 10 in Radiology by a team of investigators from the Veneto Institute of Oncology in Padua, Italy. Their results add further evidence to the growing knowledge base that supports using DBT in population-based breast cancer screening programs.

DBT is known to increase cancer detection while maintaining a lower recall rate than DM alone. And, when DBT is paired with SM – a technique that uses DBT data to reconstruct 2D images – the radiation exposure drops, making DBT a viable screening option. But, there has been little research into the outcomes of using DBT for screening programs.

That’s what the team, led by Francesca Caumo, M.D, from the Veneto Institute breast radiology department, set out to explore in their Verona Pilot Study. Could they determine the validity of DBT as a screening test instead of traditional mammography?

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“An organization needs two things to improve the results of a screening program,” Caumo said. “It needs a better first level test and a way to overcome the effect of breast density to define the risk of a patient. The Verona Pilot Study wants to answer the first point.”

To figure it out, Caumo’s team enrolled 34,638 women in their study, and 32,870 underwent repeat breast cancer screening. The average age of the study population was 58 years, and 16,198 women underwent DBT with SM. Another 16,672 had full-field digital mammography (FFDM) alone. Half of the group were re-screened two years later with DBT and SM, and the other underwent only mammography.

According to their results, DBT – in both rounds of screening – detected a higher proportion of early-stage cancers than were identified with DM. DBT and SM found 322 cancers, and DM found 153 on first screening; 131 cancers and 59 cancers, respectively, on subsequent screening. In particular, the cancer detection rate was 8.1 per 1,000 for re-screening with DBT and SM, and it was only 4.5 per 1,000 with mammography re-screening. There was not, however, a difference in the recall rate at re-screening with both DBT and SM and DM.

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In addition, with DBT and SM combined, the proportion of tumors stage II and above at re-screening was 14.5 percent compared to 8.5 percent with mammography.

Recall Rates, CDRs, and PPV1s Between the Verona Pilot Study First Round (DBT+SM) and the FFDM Control Group

ParameterControl Group: FFDMVerona Pilot Study: DBT+SMP Value
Recall rate (%)4.8 (1,389/28,680)3.9 (1,344/34,638)<.01
CDR (per 1,000 women screened)5.3 (153/28,680)9.3 (322/34,638)<.01
PPV1 (%)11.0 (153/1,389)24.0 (322/1,344)<.01

Note: The control group underwent FFDM, and the patients in the Verona Pilot Study underwent initial imaging with DBT+SM. Numbers in parentheses are numbers of women. CDR = cancer detection rate, DBT = digital breast tomosynthesis, PPV1 = positive predictive value of recall, SM = synthetic mammography.

“The lower number of stage II or above cancers with the DBT plus synthetic mammography screening test demonstrates that DBT has the capability of anticipating the detection of cancers that might become advanced in the following two years,” Caumo said. “This gives a higher benefit to our patients.”

Overall, the team said, their results are consistent with other studies that have reported higher cancer detection rates with DBT than with full-field digital mammography following two rounds of screening.

This study did have its limitations, the team said. Not only was it a single-institution investigation, but it was also not a randomized study. In addition, the study power was reduced in the repeat screening round because the population was divided for imaging with the two modalities. Data on interval cancers was also not available at the time of data analysis, stymying efforts to analyze diagnostic accuracy.

Still, according to Min Sun Bae, M.D., Ph.D., associate professor of radiology at Inha University Hospital and School of Medicine, the results of this study are strong because the authors compared the screening performance of DBT and full-field DM over consecutive screening rounds in a large prospective population-based study.

“The results of this study are important because the authors showed that the improved outcomes with DBT are sustainable beyond baseline screening, and that early invasive cancers are more often detected with DBT plus SM than with [full-field DM] at both baseline and subsequent screenings,” she said in an accompanying editorial. “Improving early detection of invasive cancer can help mitigate against overdiagnosis in mammography screening.”

She agreed that these results suggest that DBT could potentially improve the detection of clinically significant breast cancer in consecutive screening rounds, but she stressed that the results must be validated with future randomized controlled trials.

Caumo’s team does have a next step planned for the Verona Pilot Study. Their goal is to complete an analysis of interval cancers. In addition, as part of the Risk Based Screening (RiBBS) project, the team will investigate the impact of incorporating volumetric breast density measurements into a patient’s risk profile. In this project, 10,000 women will undergo DBT with SM screening, and those with breast density above a particular threshold value will be asked to undergo supplemental ultrasound.

The goal, Caumo said, is to show that a personalized model for screening is more effective than a one-size-fits-all program with no risk stratification. This could lead to identifying which women could benefit most from biennial low-risk screening and who would be best served by annual screening designed for intermediate and high-risk women.

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