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Breast cancer screening: Does tomosynthesis augment mammography?

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ABSTRACT

Digital breast tomosynthesis (DBT) is a relatively new imaging technology that is being adopted widely for breast cancer screening. Initial evidence suggests that it may reduce recall rates and increase cancer detection rates when added to digital mammography screening. However, more rigorous, prospective studies are needed to determine whether it improves long-term clinical outcomes of breast cancer screening.

KEY POINTS

  • DBT creates 3-dimensional images of the breast that the radiologist can view slice by slice, as in other cross-sectional imaging examinations.
  • Initial studies suggest that, when used in conjunction with standard 2-dimensional digital mammography as a screening test, DBT can reduce recall rates and increase cancer detection rates, but its impact on breast cancer mortality rates and cancer stage at diagnosis is not known.
  • Drawbacks of DBT: it exposes the patient to more radiation, takes the radiologist longer to interpret, and costs more than standard digital mammography alone.
  • Not all insurance companies cover DBT for breast cancer screening.
  • Dr. Lee has received research grant funding from GE Healthcare. Dr. Lee’s time is supported in part by the American Cancer Society (126947-MRSG-14-160-01-CPHPS).
  • The views expressed in this article are those of the authors and do not necessarily represent the views of the US Department of Veterans Affairs or the University of Washington, Seattle.


 

References

Each year, millions of women undergo mammography in the hope of decreasing their risk of dying of breast cancer. The effectiveness of screening mammography, however, continues to be debated.

While most randomized controlled trials have demonstrated significantly lower mortality rates in women who undergo screening, not all trials have. Most experts agree that screening mammography programs decrease breast cancer mortality rates by 12% to 33%.1,2 But some point out that although mammography programs clearly detect more cases of breast cancer, some proportion of this detection may include “overdiagnosis” of cancers that would not have caused morbidity or mortality, including ductal carcinoma in situ. Also, although deaths from breast cancer have decreased in the United States, at least some of the decrease may be due to more effective treatment rather than early detection.

Moreover, screening has well-documented harms. False-positive results cause alarm and expose women to needless follow-up imaging and biopsies, with their attendant inconvenience, discomfort, risks, and costs. Conversely, false-negative results (especially common in women with dense breasts) lead to missed diagnosis and a false sense of security.

How could programs and technology be improved to make screening more beneficial, both for patients and for society as a whole? A major improvement would be if mammography could be made more sensitive and specific for detecting invasive cancers, with fewer false-positive results. Lower cost and less frequent screening would also be major improvements.

Digital breast tomosynthesis (DBT), also known as 3-dimensional (3D) mammography, may be a way to improve the value of breast cancer screening programs. In 2011, the US Food and Drug Administration (FDA) approved DBT for all mammographic indications, including screening.

WHAT IS TOMOSYNTHESIS?

Schematic representation of image acquisition with breast tomosynthesis
Figure 1. Schematic representation of image acquisition with breast tomosynthesis.

In DBT, the x-ray source is rotated in an arc around the patient’s breast (Figure 1), generating a 3D image.3 DBT is now routinely built into newer-generation mammography units. The 3D projections of DBT are obtained during the same breast compression required for standard 2D digital mammography. Thus, DBT requires minimal additional time on the part of the patient and the technologist.4

The 3D images are processed and sent to a viewing station, where a radiologist can interpret them next to 2D images. The radiologist has the ability to scroll through the DBT projections slice by slice, as in other cross-sectional imaging examinations. However, given the larger number of images compared with digital mammography, DBT requires more time for interpretation, interrupting the workflow. A population-based observational study suggested that combined digital mammography and DBT screening examinations take twice as long to interpret.5

The main advantage of DBT is that it can mitigate the problem of overlapping breast tissue on standard digital projections. These areas of focal asymmetry may represent suspicious masses—or merely overlapping breast parenchyma. When areas of focal asymmetry are found on 2D digital mammography without DBT, patients need to come back for further diagnostic imaging to resolve the finding.6 In addition, especially in women with dense breasts, areas of overlapping tissue can have a masking effect, obscuring small breast cancers.7

Example of masking by overlapping layers of breast tissue Images courtesy of Diana L. Lam, MD, University of Washington, Seattle.
Figure 2. Example of masking by overlapping layers of breast tissue in a 2-dimensional (2D) digital mammogram, which can be mitigated by digital breast tomosynthesis (DBT). A, the 2D mediolateral oblique view of the left breast is normal in appearance. B, the corresponding 3D DBT slice demonstrates a large area of architectural distortion (circled area with spiculated appearance) in the superior left breast that represents invasive ductal car-cinoma.

For breast cancer screening, DBT is read in conjunction with standard digital mammography. By allowing examination of the breast parenchyma in thin slices, DBT decreases the interpretive issue of overlapping breast parenchyma and the masking effect, potentially leading to fewer false-positive results and higher rates of cancer detection (Figure 2).

EFFECTIVENESS OF TOMOSYNTHESIS

There is limited evidence at this time to support the addition of DBT to digital mammography for primary breast cancer screening, with no published randomized trials that assessed outcomes. However, 2 population-based trials in Europe have prospectively assessed DBT plus digital mammography as a primary screening strategy: the Screening With Tomosynthesis or Standard Mammography (STORM) trial8 and the Oslo tomosynthesis screening trial.5 Only the STORM trial reported first-year interval cancer rates, from which the sensitivity and specificity of DBT plus 2D digital mammography could be calculated and compared with those of 2D digital mammography alone.8

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