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Sunday 19 May 2019
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Sponsored: New evidence for digital mammography plus tomosynthesis

Breast cancer accounts for one in three cancers in women throughout the European Union (EU), making it the leading cancer site among women on the continent. With a mean breast cancer incidence rate of 70.7, western Europe also has one of the highest incidences of breast cancer in the world, accounting for 11 of the top 20 countries.1–3
 
Screening is the mainstay of breast cancer detection, with numerous studies finding that early detection translates into substantially reduced mortality rates.4–6
 
However, current technologies have several shortcomings. The most common is false-positive recalls, leading to unnecessary testing and biopsy procedures. This is particularly true of women with dense breasts, which can hide a lesion, and of those with superimposition of fibroglandular tissue, which can be misinterpreted as a lesion.7,8 Getting a false positive diagnosis causes unnecessary anxiety and fear, and women who receive a false positive result are more likely to delay their next mammogram.9
 

Digital breast tomosynthesis

Digital breast tomosynthesis (DBT), the latest generation technology in breast imaging, uses a three-dimensional, limited-angle tomographic breast imaging technique to provide multiple projection views, thus reducing interference from overlapping tissues. These thin slices (at 1-mm spacing) are then reconstructed to provide the three-dimensional view. 
 
Numerous observational and clinical studies attest to the improved specificity DBT offers, whether used as an adjunct with digital mammography (DM) or synthetic 2D mammography, or as a stand-alone screening technique, as well as its ability to reduce recall rates while improving cancer detection, particularly for invasive cancers.8,10–14
 
The European Society of Breast Imaging (EUSOBI) in its most recent position paper on screening mammography concluded that DBT is set to become “routine mammography” in the screening setting in the near future, but also noted there are several unanswered questions around the technology.15
 
Areas of focus for current research include data on the challenges of implementing DBT-based screening programs; rates of overdiagnosis; cost effectiveness; and, perhaps most important, the ability of DBT to improve prognosis, mortality, and morbidity.16
 
One of the first prospective, randomised trials assessing the use of DBT in the screening context is the Reggio Emilia Tomosynthesis Randomised Trial. The study is being conducted at screening centres in northern Italy, and is designed to look at interval cancers, or those detected between screening exams, and cumulative incidence of advanced cancers.17
 
Preliminary results published recently provide additional evidence regarding the benefits of DBT + DM versus DM alone. This two-arm, test-and-treat prospective randomised trial compared DM plus DBT (experimental arm) with DM alone (control) in 19,560 women aged 45–70 who had previously received one round of screening and had no familial risk of breast cancer. All screening mammograms were conducted using GE mammography equipment, including tomosynthesis. Figure 1 (refer to the next page) highlights the study design and randomisation. 
 
Figure 1: Flowchart of recruitment phase and study design
 
Figure 1: Flowchart of recruitment phase and study design
 
The authors reported a detection rate 90% higher in the DBT + DM arm than in the control arm (8.6 per 1000 women screened vs 4.5 per 1000 screened), with similar recall rates. The detection rate was higher for ductal carcinoma in situ (DCIS) than invasive cancer; for invasive cancers <10mm (84% increase) and ≥10–20mm (122% increase); and for grade 1 and 2 cancers. The overall detection rate was slightly higher than that seen in other recent European studies, the authors noted, and significantly higher than those seen in US observational studies.11,13,17–21
 
Most of the gain in invasive cancer detection (72 out of 80) observed in the experimental arm was due to DBT alone (Figure 2). Thus, the use of DBT alone could reduce the higher dose seen in the experimental arm by avoiding double exposure.22 The investigators also reported a 25% lower rate of false-positive results in the experimental group than the control group, and a roughly 70% increase in detection rate in women with dense breasts compared with DM alone.17
 
Figure 2: Cancers detected with DBT only
 
Figure 2: Cancers detected with DBT only
 
The number of DCIS lesions was higher in the experimental group (+1 per 1000), as were benign lesions and lesions of uncertain malignant potential referred for excision (+0.5 per 1000).17 Although there is debate regarding the increased rate of DCIS diagnosis that has occurred with screening mammography, there is also substantial evidence that DCIS is a precursor to invasive cancer.23,24
 
While there was a 70% longer reading time for DBT + DM versus DM alone, the increase was related to positive studies, suggesting it resulted from the need to review multiple images, not the interpretation itself. Variability between readers was similar in both arms.17
 
Figure 3: DBT vs digital mammography: Detection by cancer size
 
Figure 3: DBT vs digital mammography: Detection by cancer size
 
“Our data confirms the excellent results of 3D mammography, previously evidenced in other European prospective studies carried out on large-population screening programs,” said the lead investigator, Pierpaolo Pattacini, MD. “But our results go a step further: only randomised trials can evaluate the effectiveness of a new screening technology, like whether it can save more lives.” 
 

Conclusions

The body of evidence as to the ability of DBT + DM to identify significantly more lesions with fewer false-positives and similar recall rates compared with DM alone continues to expand. Several large, multicentre clinical trials are currently underway that will, hopefully, answer some of the remaining questions currently preventing the greater adoption of DBT in the clinical setting. 
 

References

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18 Skaane P et al. Prospective trial comparing full-field digital mammography (FFDM) versus combined FFDM and tomosynthesis in a population-based screening programme using independent double reading with arbitration. Eur Radiol 2013;23(8):2061–71.
19 Lang K et al. Performance of one-view breast tomosynthesis as a stand-alone breast cancer screening modality: results from the Malmo Breast Tomosynthesis Screening Trial, a population-based study. Eur Radiol 2016;26(1):184–90.
20 McDonald ES et al. Effectiveness of digital breast tomosynthesis compared with digital mammography: Outcomes analysis from 3 years of breast cancer screening. JAMA Oncol 2016;2(6):737–43.
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