Improved Performance With 3D Mammography

Veronica Hackethal, MD

February 25, 2016

A single-center study has shown improved performance for digital breast cancer tomosynthesis (DBT) compared with standard digital mammography.

The study, published online February 18 in JAMA Oncology, is the first to report on DBT screening results over several years.

"Although DBT was initially implemented without knowledge of long-term performance, this is, to our knowledge, the first evidence that sustained and even improved performance is possible with consecutive DBT screening," say lead author Emily F. Conant, MD, chief of breast imaging in the Department of Radiology at the University of Pennsylvania, in Philadelphia, and colleagues.

However, in an accompanying editorial, Diana Miglioretti, PhD, Dean's Professor in Biostatistics, University of California, Davis, School of Medicine, and Nehmat Houssami, MBBS, FAFPHM, PhD, University of Sydney, point out limitations to the study's findings.

"We need more research to identify which women may benefit from this new technology that's more expensive and has greater radiation exposure and which women may not need it," Dr Miglioretti told Medscape Medical News.

Already Implemented in Many Centers

DBT, also known as 3D mammography, provides a three-dimensional view of the breast. It received approval from the US Food and Drug Administration in 2011. Since then, many centers in the United States and Europe have implemented DBT, even though important research gaps still exist. Data on long-term performance, mortality benefits, and cost-effectiveness are lacking.

Theoretically, DBT can distinguish normal from cancerous tissue better than digital mammography. Past studies have suggested that DBT can improve false positive and false negative rates, increasing cancer detection and decreasing patient recalls.

Drawbacks include potential detection of clinically insignificant cancers and twice the radiation dosage of digital mammography. DBT also costs more than standard mammography.

Study Details

Results from the study were originally presented at the Radiological Society of North America 2015 Annual Meeting.

For their study, Dr Conant and colleagues conducted a retrospective analysis of all patients without a past history of breast cancer (n = 23,985; mean age, 56.8 years) who underwent screening mammography (n = 44,468) at the University of Pennsylvania from September 2010 to September 2014. The medical center transitioned from digital mammography to DBT in September 2014. Women who underwent screening prior to this date received digital mammography only (year 0). From October 2011 through September 2014 (years 1-3), women received two-view digital mammography and adjunctive two-view DBT.

Results showed a slight increase in recall rates for years 1, 2, and 3 of DBT (88, 90, and 92 per 1000 patients screened, respectively), though the difference across these years was statistically nonsignificant (P = .55). Recall rates for DBT across these years were significantly lower than recall rates for digital mammography alone (104 per 1000 patients screened).

DBT also appeared to detect more cancer cases in recalled patients. Cancer cases in recalled patients rose from 4.4% with digital mammography alone to 6.2% (P = .06), 6.5% (P = .03), and 6.7% (P = .02) with DBT in years 1, 2, and 3, respectively. The number of cancer cases in recalled patients during years 2 and 3 of DBT differed significantly from the number identified with digital mammography alone (P = .03 and P = .02, respectively). The difference across the three DBT years was not statistically significant (P = .92).

Rates of interval cancers — those detected between scans ― declined slightly, at 0.5 per 100 women screened with digital mammography compared with 0.7 per 100 women screened in year 1 of DBT, but the difference was not statistically significant (P = .60).

Limitations include the study's nonrandomized, observational design and the inability to assess family history in some patients. Researchers are currently undertaking a cost-effectiveness analysis.

We believe this represents the first longitudinal analysis of women recalled for further DBT screening. Dr Emily Conant and colleagues

"Despite limitations, we believe this represents the first longitudinal analysis of women recalled for further DBT screening and is an important initial step toward informing policies for possibly integrating this technology into population-screening programs," the authors conclude.

In the editorial, Dr Miglioretti agrees that the study "provides new data to fill some of the existing evidence gaps," but she notes that it "does not shed light on whether adjunct DBT will extend screening benefit beyond improving screening performance measures."

The study offers preliminary evidence by showing a decrease in interval cancer rates (which can indicate the benefit of early detection), but the decrease occurred only after the first year, Dr Miglioretti told Medscape Medical News. Longer follow-up is needed to determine changes in interval cancer rates with DBT, she said, and because DBT is still a new technology, those data are not yet available.

Likewise, this study offers some evidence for sustained decrease in recall rates for women without dense breast tissue but not for women with dense breast tissue, whose recall rates started to rise again and were no longer significantly different from those patients who underwent digital mammography after the first year, she pointed out.

"An important and possibly worrisome finding is the drop in recall rates not holding up for women with dense breast tissue," she said.

Given that about 27.6 million US women aged 40 to 74 years have dense breasts and that about 10% to 12% of US women who undergo screening mammography need to return for more imaging, the number of women who do not benefit from DBT could really add up, she continued.

Generalizability is also a concern.

"Most women in the US receive screening in community practice with mammograms read by general radiologists, not breast imaging specialists at academic medical centers," she said, "We can't take away from a single study how well this new technology does. We really need larger studies with a large number of diverse facilities to make sure the findings hold up in those settings."

Dr Miglioretti advises caution in the rapid rollout of this new technology. Although DBT offers the hope of an increase in detection rate of clinically meaningful cancers, as well as a drop in interval cancer rates and a sustained recall rate, the advantages are not clear because of limited evidence from general community practice.

Dr Weinstein and Dr Conant have consulted for Siemen's Healthcare. Dr Conant is a paid scientific advisor and lecturer for Hologic Inc. Dr Houssami and Dr Miglioretti have disclosed no relevant financial relationships.

JAMA Oncol. Published online February 18, 2016. Abstract, Editorial


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