3D mammograms show benefits over 2D imaging, especially for dense breasts

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Three-dimensional imaging outperformed older digital mammography at reducing anxiety-producing callbacks for more breast cancer testing, a new study shows. The research, published this month in the journal Radiology also suggests the newer technology might find more worrisome cancers earlier during routine screenings.

Lead author Dr. Liane Philpotts, a Yale School of Medicine radiology professor, hailed 3D mammography, also known as digital breast tomosynthesis or DBT, as “a win, win, win.”

“We have the benefit of a lower recall rate, or fewer false positives. We have increased cancer detection, and we have a lower rate of advanced cancers,” she said. “So it’s truly a game changer.”

DBT machines take multiple cross-sectional radiographic images of different angles of the breast, allowing radiologists to evaluate the tissue layer by layer. The improved visibility can be especially helpful for dense breasts.

Still, the new study, fails to definitively answer the question of whether newer, more expensive 3D mammography finds troublesome breast cancers earlier than 2D mammography, sparing women harsh treatment and saving lives, an accompanying editorial says.

The verdict won’t come until 2030, at the conclusion of a large-scale randomized controlled trial comparing 3D to 2D mammography, according to the editorial written by two Korea University Guro Hospital radiology professors.

Pending the 2030 trial results, the editorial concludes, the new study provides “indirect evidence suggesting the potential of DBT screening in improving survival outcomes.” 

The U.S. Food and Drug Administration approved digital breast tomosynthesis as a breast-imaging method in 2011.

As of this month, 91% of mammography facilities in the U.S. had at least one DBT system, and 48% of all mammography machines were DBT, according to the FDA, which inspects the facilities.

The new study evaluated breast cancer cases detected with screening mammography over 13 years, the first three years with 2D digital mammography and the next 10 years with 3D, at Yale, an early adopter of 3D mammography. It is the largest study to date to compare the two modalities, with nearly 240,000 mammograms using 3D and nearly 36,000 using 2D.

Radiologists detected significantly more breast cancer in the 3D group compared to the 2D group, and the 3D group was called back less often for more breast cancer testing, in 7.2% of cases compared to 10.6% of cases for 2D, the study found.

The most important finding, the study authors said, was that 3D mammography found a lower proportion of advanced cancers, 33% compared to 44% with 2D mammography. “We’re finding more cancers, but they’re at a lower stage,” Philpotts said. “We’re finding them earlier.”

Jeffrey Tice, a professor of medicine at the University of California, San Francisco, who is working on a personalized approach to breast cancer screening, remains unconvinced. The women in the Yale study who were screened with 3D mammography were older and waited longer between mammograms – differences the authors failed to consider in their calculations and conclusions, he noted.

“The real question is whether tomosynthesis is picking up cancers earlier that were going to grow and turn into advanced cancers,” he said. “And I don’t think this study answers that question.”

Like the writers of the editorial, he believes that only the ongoing randomized controlled trial can determine the true benefits of 3D over 2D mammography.

Previous studies have suggested that although 3D mammography might improve the detection of advanced cancer, it might also lead to overdiagnosis.

One clear benefit of 3D mammography, though, on which Tice and Philpott agree is that the newer technology prevents false alarms, callbacks for more mammography to determine whether something on an X-ray is indeed a problem, especially in younger women with dense breasts.

In 2D mammography, radiologists might see something questionable, but when they look at 3D images, they can rule out problems and avoid callbacks, which lead to additional, sometimes unnecessary, tests and stress.

Whenever possible, Philpott recommends that women request 3D mammography. But she acknowledges that women with dense breasts, generally pre-menopausal women, will benefit most from tomosynthesis.

“Any time there’s a little bit more tissue density,” she said, “it can obscure cancers, and it also leads to false recalls.”

 Ronnie Cohen is a San Francisco Bay Area journalist focused on health and social justice issues.