Ultrasound turned in a better incremental breast cancer detection rate than tomosynthesis in mammography-negative dense breasts, and a similar false-positive rate, according to interim findings from the ASTOUND trial.
During 2012-2015, the multicenter Adjunct Screening With Tomosynthesis or Ultrasound in Women With Mammography-Negative Dense Breasts (ASTOUND) trail screened 3,231 dense-breasted asymptomatic women (median age 51) with negative mammograms using both tomosynthesis and physician-performed ultrasonography.
Among more than 3,000 mammography-negative screening participants with dense breasts, 24 additional breast cancers (BC) were detected, of which 23 were invasive. All 23 were detected with ultrasound for an incremental cancer detection rate (CDR) of 7.1 per 1,000 screens (95% CI 4.2-10.0, P=0.006) versus 13 found with tomosynthesis (incremental CDR 4.0 per 1,000 screens, 95% CI 1.8-6.2), reported Nehmat Houssami, MBBS, MPH, PhD, of the University of Sydney, and colleagues. This study was recently published in the Journal of Clinical Oncology and presented at the 1oth European Breast Cancer Conference.
“Our results could be taken to suggest that tomosynthesis is detecting [breast cancers] that would have been otherwise masked (on 2D mammography) by overlapping breast parenchyma, but seems less capable than ultrasound at finding cancers that are entirely masked by mammography-dense tissue,” Houssami’s group wrote. “We assume that some cancers are visible to only one of the physical principles of imaging modalities (x-ray for tomosynthesis vs ultrasound).”
The majority of ultrasound-detected cancers undetected by tomosynthesis were masses, whereas the single malignancy detected by tomosynthesis but missed by ultrasound was an architectural distortion.
The authors pointed out that these results are interim only, and relate to a self-referring population of women with dense breasts and negative mammograms.
One of the historical barriers to implementing ultrasound (US) breast cancer screening in practice has been the high rate of false-positives, explained Wendie Berg, MD, PhD, of Magee-Womens Hospital of University of Pittsburgh Medical Center, in an accompanying editorial.
“Importantly, in preliminary results from the ASTOUND trial, false-positive recalls (2.0%) and biopsies (0.7%) were acceptably low,” she noted.
However, she pointed out that “these low rates likely reflect that most of the US screens in ASTOUND were incident screens (with prior examinations available); further, recommendations for short interval follow up (Breast Imaging-Reporting and Data System density categories three) were not considered test positive.”
But Berg suggested that the two modalities can work together. “On the basis of the results from ASTOUND, tomosynthesis still misses a substantial number of invasive cancers in women with dense breasts: supplemental US after tomosynthesis would still be reasonable, although further study is warranted,” she wrote.
Bottom line: The combination of 3D tomosynthesis mammography and whole breast ultrasound significantly improves breast cancer detection in women with “dense” breasts.
