Screen-Detected Breast Cancer Rates Similar With Digital Breast Tomosynthesis, Digital Mammography

Breast cancer detection is similar with digital breast tomosynthesis (DBT) or standard digital mammography, though DBT may reduce recall rates, researchers say.

“We expected, based on results from other studies, a higher detection rate in the DBT-arm,” Dr. Solveig Hofvind of the Cancer Registry of Norway told Reuters Health by email. “The results were thus somewhat controversial and need explanation. Our study illustrates the complex interplay between new techniques and human readers in high-volume screening, and the challenges related to implementation of new technology.”

“Our study was performed in a real-world setting in a high-volume screening program,” she noted. “Independent double batch reading was performed, followed by consensus, according to the European guidelines. About half of cases were dismissed at consensus. This procedure is typical in most European countries, but differs from most screening procedures in the U.S.”

Further, “the study was performed using first generation DBT equipment, and the radiologists had limited experience in screen-reading DBT when the study started, which is natural,” she said. “The order of the reading and the type of images used might have had an effect on the interpretation.”

“An extensive hanging protocol and pressure to perform efficiently might have affected the number of cases discussed, and dismissed, at consensus,” she added. “Further, findings on DBT might have been present and perceptible by radiologists on the previous digital mammogram, but considered non-suspicious or positive, but dismissed on the consensus.”

“The radiologists were blinded to the results from interim analyses – no feedback was given if the results were in line with the recommended values in BreastScreen Norway,” she added. “Experience shows that feedback to radiologists can impact their performance.”

Dr. Hofvind and colleagues randomized close to 30,000 women ages 50-69 to DBT or digital mammography screening.

As reported online May 8 in The Lancet Oncology, after exclusions, a total of 28,749 were included in the analyses. The proportion of screen-detected breast cancers did not differ between the two groups: 0.66% in the DBT group versus 0.61% in the digital mammography group (RR 1.09). Further, after a consensus meeting, the proportion of biopsies did not differ between the groups: 1.8% for DBT versus 1.9% for digital mammography.

However, the likelihood of recall was lower for DBT (RR, 0.78).

The authors conclude, “Economic analyses and follow-up studies on interval and consecutive round screen-detected breast cancers are needed to better understand the effect of digital breast tomosynthesis in population-based breast cancer screening.”

Dr. Hofvind said, “We are now running a two-year trial ending in 2019, where all women are offered DBT (using upgraded equipment). The aim is to compare rates of interval- and screen-detected breast cancer. Mammographic features and histopathological findings will be carefully analyzed, and a radiological review of prior mammograms of interval- and screen-detected cancers will be a part of the follow up.”

Dr. Sophia Zackrisson of Skane University Hospital, Lund University in Sweden, commented by email, “Going forward, the combination of a radiologist and artificial intelligence may help avoid some of the difficulties pinpointed in the trial that are likely to occur in other clinical settings.”

“On the positive side, recalls were lower and there was a higher positive predictive value for those recalls with digital breast tomosynthesis compared with digital mammography, as was found in many of the retrospective trials conducted in the U.S.,” she told Reuters Health.

“As the first randomized, controlled trial with digital breast tomosynthesis in a real-world, population-based screening program, this study contributes to our understanding of digital breast tomosynthesis in breast screening, provides evidence-based findings on its early implementation, and has the potential to contribute valuable information on interval cancers.”- Medscape