A new ten-year study found that when breast cancer screening is performed with digital breast tomosynthesis (DBT), it improves cancer detection and reduces the rate of advanced cancers, compared to 2D digital mammography. The results were published yesterday in Radiology.

"When we looked at women who had subsequent rounds of DBT screening, the metrics improved even more — whereas with 2D mammography, it did not change," Dr. Liane Elizabeth Philpotts, first co-author and professor of radiology and biomedical imaging at Yale School of Medicine, told HCB News. "So repeated imaging with DBT does even better."

For the study, Philpotts and her team evaluated consecutive cancer cases detected by screening mammography over 13 years at Yale University/Yale-New Haven Health. That included 10 years of mammograms performed with DBT and three years with digital mammography.
Altogether, that included 272,938 screening mammograms — 35,544 performed with digital mammography and 237,394 with DBT. A total of 1,407 cancers were detected, 142 with digital mammography, and 1,265 with DBT.

They found that DBT had a cancer detection rate of 5.3% and digital mammography had a rate of 4%. DBT had a lower rate of advanced cancers — 32.7% versus 43.6% — which means that cancers are likely being detected earlier.

In addition, most of the true-positive cancer cases detected by DBT presented as masses, as opposed to calcifications and asymmetries. The recall rate was also lower for DBT compared to digital mammography — 7.2% versus 10.6%.

Philpotts explained that skeptics of mammography screening believe that the use of DBT leads to overdiagnosis. That's because many early studies that looked at DBT showed a slightly higher cancer detection rate, but many of those additional cancers were low-grade, luminal cancers.

"If that was consistently the case then one could think that DBT was overdiagnosing, as finding slow growing nonaggressive cancers that may not affect a woman's outcome could be considered undesirable," she said. "It is important for mammography screening to detect cancers that are potentially lethal and that’s why it was so important to look at long term data."

She and her team found that the subtypes of cancers were, overall, similar between digital mammography and DBT, meaning DBT did not have a higher rate of low-grade cancers. In addition, the rate of advanced cancers was lower, which is important because some cancers are more aggressive and finding them at an early stage is desirable, she said.

DBT has been the standard of care at Yale facilities since 2011 and it's quickly becoming the standard in the rest of the U.S. as well, according to Philpotts. She thinks that all facilities will eventually swap out their older 2D machines with DBT because she believes it's "simply a better mammogram."

However, this is not the case in other parts of the world. Many countries, especially those with population-based screening programs that are limited by financial constraints, required proof that DBT is better in terms of patient outcomes.

"DBT machines are more costly and it takes longer for radiologists to interpret the images, so there are cost considerations involved," said Philpotts. "The added costs have to be balanced with better patient outcomes. Our study certainly suggests that patient outcomes will be improved with fewer advanced cancers being diagnosed."

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