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URBANA — The option of using newer-technology 3D mammography to screen for breast cancer has been around for much of the past decade. But it still comes with a big unknown.

That is, do 3D mammograms find more of the breast cancers that are likely to be life-threatening than standard 2D mammograms do?

Researchers are hoping to learn more about that in a National Cancer Institute study that's underway across the country.

Hundreds of local women are participating in the Tomosynthesis Mammographic Imaging Screening Trial, or TMIST for short, through the Carle Cancer Center in Urbana, and Carle is preparing to expand the study to Vermilion County in July.

Since the first 3D mammograms were approved in 2011, women have been offered a choice when they schedule these screenings — to stick with the traditional 2D or opt for 3D. But there isn't enough information available to make an informed choice, according to oncologist Dr. Kendrith Rowland, the principal investigator for the study at Carle.

A 3D mammogram, which combines multiple images to create a three-dimensional view of each breast, is very sensitive, he said.

But while 3D may result in more biopsies, more cancer detections and less need to recall women for further testing, he said, it also comes with both higher radiation exposure and higher cost, along with this uncertainty: Are there women who would do just as well with the 2-D?

"The problem is that 3D promotes itself as finding more cancers, but is it really finding cancers that will result in mortality?" he asked.

Currently, mammogram screening guidelines are largely based on age, rather than being personalized according to what's best for each woman, Rowland said. Those guidelines advise women to begin mammograms at age 45 and continue them annually or every other year, depending on their age and preferences.

"Women are coming in for screening, but we really don't know what's the best screening for women — and it could depend on their demographics, their genetic background, a whole host of other issues," Rowland said.

Through the TMIST trial, researchers hope to learn more about whether 3D mammograms are better than 2D mammograms at finding more of the potentially deadly cancers before they become more difficult to treat.

Researchers also hope to learn whether 3D mammograms result in fewer false positives and fewer harder-to-treat cancers in certain demographic groups, such as black women, those with dense breasts, those who are premenopausal and those taking hormone replacement therapy, according to the NCI.

The TMIST trial is striving to enroll 165,000 women across the U.S., and many more participants are needed, Rowland said. Carle has enrolled 863 local patients and hopes to enroll more, he said.

Participants must be between ages 45 and 74. They're being randomly assigned to receive either 2-D or 3D mammograms for five years, with how often they're screened based on such factors as age, breast density, family history of breast cancer, menopausal status, use of hormone replacement therapy and presence of genetic changes known to cause breast cancer.

Researchers plan to follow participants' health for three years after the five-year mammogram period.