A growing number of women are likely to face a similar choice in coming years as imaging centers across the country add three-dimensional (3-D) mammography, also called digital breast tomosynthesis, to the two-dimensional (2-D) screening women customarily receive.

According to the Food and Drug Administration, there were 3,915 certified mammography imaging facilities that offered digital breast tomosynthesis in January. That's a sharp increase over the previous January, when the total was 3,011.

Both types of tests use X-ray technology to create images of the breast. The 2-D digital mammograms that most women receive typically provide front and side images, while for the 3-D test the X-ray arcs across the breast, creating multiple images of breast tissue. 

Studies have generally shown that the 3-D test is slightly better at detecting cancers than the 2-D test. But the jury is still out on whether the newer technology is any better at identifying the advanced cancers that will become lethal.

"Cancers don't always progress and kill people," said Dr. Etta Pisano, chief science officer at the American College of Radiology's Center for Research and Innovation and a faculty member at Harvard Medical School.

Pisano is leading a five-year clinical trial of 165,000 women that will compare the two types of screening tests to evaluate whether the new technology reduces the risk that women will develop life-threatening cancers.

"If tomosynthesis is improving the likelihood of women to survive their breast cancers, they should have fewer cancers that are more likely to kill women over the 4.5 years of screening. Since tomosynthesis caught them early, they'll never grow up to be bad cancers," Pisano said.

Overdiagnosis is one of the potential downsides of this technology, said Dr. David Grossman, chair of the U.S. Preventive Services Task Force. Some research suggests the biopsy rate is slightly higher with 3-D mammograms.

In addition, some of the mammography systems require both 2-D and 3-D X-rays, which can expose women to twice as much radiation. The 2-D image is important because clusters of calcifications, which may signal breast cancer, might be easier to see on the 2-D image, said Pisano.

Insurance coverage of 3-D testing has improved in recent years, but it's not assured. The 3-D test typically costs about $50 more than a 2-D test, according to a 2015 study by Truven Health Analytics that was funded by Hologic, a manufacturer of 3-D mammography systems. Medicare also covers 3-D tests.

"If the examination is available at no extra cost, the data we have now tells us it has some advantages," said Smith. On the other hand, "any woman who's feeling stressed about the extra cost … should feel comfortable getting a regular mammogram," he added.