Twelve years ago, the FDA approved Hologic’s digital breast tomosynthesis (DBT) system – sometimes incorrectly referred to as 3D mammography – as an alternative to 2D full-field digital mammography (FFDM) to screen for breast cancer. Since then, other companies have introduced DBT systems, with the FDA reporting there are now 24,707 accredited mammography systems in the USA, and FFDM units (13,332) slightly outnumber DBT units (11,375). However, a key question still needs to be answered: Does DBT perform better than FFDM to justify the significant extra cost?
This is an important question, considering that this week the FDA set national standards to protect women with dense breast tissue, and one of the claimed benefits of DBT is that it detects cancers not seen with FFDM. A paper published earlier this week in Radiology (click here) has provided evidence to suggest that DBT is perhaps slightly superior to FFDM. Dr Emily Conant, chief of breast imaging at the University of Pennsylvania (seen above right) compared FFDM and DBT for four key parameters: recall rate; cancer detection rate per 1,000 women screened; positive predictive value (PPV) of recall; and biopsy rates (per 1,000).
She and her colleagues, who included two Hologic employees, completed a retrospective cohort study that included women aged 40 to 79 years who underwent FFDM or DBT screening over a 7-year period, beginning January 2014. There were five study sites and a total of 2.5 million examinations (1.7 million DBT, and 0.8 million FFDM) of 1.1 million women. The main findings are summarised in the table at left, where the differences between FFDM and DBT are all statistically significant at the 0.001 level.
As seen, the recall rate for DBT is lower than for FFDM, while the cancer detection rate is slightly higher. The PPV for recall is greater for DBT, as is the biopsy rate for 1,000 women screened. These findings are presumably why Conant told AuntMinnie.com: “This study further substantiates that DBT should be the standard of care for mammographic screening.”
The authors did not reference the TMIST trial, funded by the National Cancer Institute to the tune of $100 million, that is yet to be completed, and was designed to see if DBT is better than FFDM for reducing advanced breast cancer. They also argued the inclusion of false-negative results for both imaging modalities rarely overestimates cancer detection rates, but we know this is not the case. In fact, both DBT and FFDM in particular, have sensitivities less than 100%, especially for dense breasts. So, is DBT there yet? Maybe.