Here is Lora Barke, DO answering RSNA’s questions regarding her recent research on Digital Breast Tomosynthesis.
What are the chief limitations of mammography?
The ideal screening tool finds all the cancers and causes no false alarms- so our goal is to get as close to that ideal as we can. On regular 2D mammography, a big limitation is overlapping tissue because the breast is just compressed into one flat image, which can not only result in recalls from screening mammography, it can also hide cancers.
With DBT, we have the ability to scroll through the breast tissue a millimeter at time and unmask these areas. As a result, many studies, including ours, have shown that recall rates decrease and cancer detection increases when DBT is used. Our study furthermore shows a significant increase in sensitivity as well as specificity- essentially showing that with DBT, we are better at finding a cancer when a cancer exists, and can be more confident when we say that an exam is normal. With DBT, we come closer to the ideal.
How are false negative asymptomatic cancers discovered?
If a patient has another kind of screening in addition to mammography, like ultrasound or MRI, and a cancer is found within 12 months of a negative mammogram, these are called asymptomatic FN cancers. In our study, we also included exams that were categorized as BIRADS 3 but ended up being cancer within 12 months.
Symptomatic false negative cancers are those that present with a symptom like pain, discharge, or a lump, within a year of a normal mammogram. These are often more aggressive- they grow faster and have poorer biologic profiles compared to cancers detected at screening.
What do these results suggest about the role of DBT going forward?
Using false negative cancer rates is a way to get an idea of how a tool can affect morbidity/mortality, in a more reasonable time frame than a randomized clinical trial. Here, we have shown a trend towards fewer false negative cancers with DBT. Our results build on past studies that have shown that DBT improves performance outcomes for breast cancer screening- with DBT, we show we are detecting more invasive cancers, but they are cancers with favorable prognostic criteria, which means these patients would have more treatment options. Taken together with reduced recall rates, and thus less patient anxiety, I would anticipate that DBT will continue to move forward as the standard of care to replace regular mammography.
Are there any drawbacks to DBT that need to be addressed before it can have a more widespread role?
DBT equipment does cost more but reimbursement is also higher by most insurances, so the return on investment is rapid. Also, multiple studies have shown that screening outcomes are significantly improved with DBT, which translates to more efficient workflow: because there are fewer recalls, fewer additional studies need to be done, and when an abnormality is found on DBT, the work up or evaluation of the finding usually needs less additional imaging or can go straight to ultrasound, compared to abnormalities detected on 2D alone.
There may be some practices that are waiting to switch to DBT because of radiation dose concerns. While there is more radiation dose when a study is performed with DBT, it is still below FDA safety limits. Synthesized DBT creates a 2D image so you don’t have to take a regular 2D mammogram picture and this essentially halves the radiation dose and makes it the same dose as regular mammogram. Studies are showing that this synthesized DBT also has similar benefits as the original DBT, though we don’t have as much evidence yet with synthesized DBT.
Does DBT have any advantages in imaging dense breasts?
In our current study, Recall rates were significantly lower in both heterogeneously dense and extremely dense breasts in the DBT group compared to DM. We also saw significantly higher cancer detection rates with DBT in women with heterogeneously dense breasts compared to DM. With women with extremely dense breasts, the cancer detection was higher, but not significantly so. Which makes sense- you need a bit of fat to provide contrast to the fibroglandular tissue in order to detect abnormalities, whether you are using DBT or DM. And this highlights a group of women who would benefit from supplementary screening.
Learn more here-https://pubs.rsna.org/doi/10.1148/radiol.2020202858