By Nina Agrawal
The New York Times
Women going in for routine mammograms are increasingly being screened with a new type of imaging tool: digital breast tomosynthesis.
The new technology, which is sometimes referred to as 3D mammography or DBT, lets doctors look at the breast in greater detail. Some research has shown that it can detect slightly more cancers with fewer false-positive results than conventional mammograms — although it’s still too early to know whether these benefits will translate to fewer cancer deaths.
“By the time we know the answer, this will already be the default technology,” said Dr. Ilana Richman, an assistant professor at the Yale School of Medicine who has studied adoption of the procedure across the United States. Almost half of all mammography units in the country are now tomosynthesis units, and more than 90% of all breast imaging facilities in the country offer the procedure, according to federal data.
How does tomosynthesis work?
The procedure is similar to a regular mammogram, when the breast is compressed between plates and a machine takes X-rays. But in DBT, a machine takes multiple X-rays across the breast and reconstructs them into slices to create a quasi-3D picture. In contrast, traditional mammography takes one X-ray of the entire breast from a top view and another from a side view and creates a 2D picture.
Doctors often compare it to looking at slices of bread. “Digital breast tomosynthesis allows us to deconstruct the breast into layers to make it easier to see,” said Dr. Kathryn Lowry, an associate professor of radiology at University of Washington School of Medicine and a physician at Fred Hutch Cancer Center.
Seeing those additional layers can sometimes help reveal potentially cancerous masses hiding behind other tissue — or make clear when an abnormality is actually nothing, Richman said.
What are the benefits?
Several studies have shown that DBT finds a few more cancers than traditional mammography, Lowry said.
The cancer detection rate of a routine, traditional mammogram is about 4 to 6 cancers per 1,000 women, Lowry said. DBT has been shown to improve the detection rate by about 0.5 to 4 additional cancers per 1,000 women, she said. The detection rates depend on the setting and patient characteristics, including age and breast density, and whether a scan is a person’s first mammogram.
One of the big questions among medical experts is whether detecting more cancers prevents more breast cancer deaths or simply leads to a greater likelihood of unnecessary treatment for cancers that may never have progressed.
“Are you really finding tumors that have a clinical impact, or is it more overdiagnosis?” said Dr. Karla Kerlikowske, a professor of medicine, epidemiology and biostatistics at the University of California San Francisco.
We don’t know yet whether the DBT scans reduce breast cancer deaths. Kerlikowske’s research, based on data from more than 1 million patients, suggests that DBT may benefit those who are both at high risk for breast cancer and have extremely dense breasts. In these patients, her research suggested that DBT catches aggressive cancers earlier than a traditional mammogram would.
The most convincing evidence in favor of DBT, experts said, is that it reduces false-positive results that require patients to come back for additional imaging — from more than 100 per 1,000 women to about 90, depending on the study.
“Even if there is no difference in cancer outcomes, that alone means it is a better test,” Lowry said.
Reducing these false positives means less patient anxiety over a possible cancer diagnosis, and eliminates the need for (and hassle of) returning for more imaging.
“If it spares you the phone call that says, ‘Hey, we found something suspicious,’ that is a real benefit to women,” Richman said.
Do doctors recommend it for everyone?
Kerlikowske, who is also a primary care physician, said that, other than the patients whom her study found specifically to benefit from tomosynthesis, the type of mammogram doesn’t matter.
Dr. Sarah M. Friedewald, a professor of radiology at Northwestern University Feinberg School of Medicine, said she would encourage everyone who can have DBT to do so. “It’s just a better mammogram,” she said. (Friedewald consults for Hologic, which makes tomosynthesis equipment.)
The U.S. Preventive Services Task Force has said that both digital mammography and DBT are effective forms of screening. The American College of Radiology has endorsed both for screening and diagnostic purposes.
How much does DBT cost?
Some states require private insurers to cover the scans without a copay, a few require coverage but allow a copay, and several states require nothing. Medicare covers screening with DBT as a free preventive service, as does Medicaid in some states.
When insurance doesn’t cover the procedure fully, the average out-of-pocket cost is about $70 to $77, according to a study Richman published in 2022.
Without insurance, the list price could be hundreds of dollars. Payment plans or state and community health screening programs can offset or eliminate that cost.
