Digital Mammography Better Than Film for Some Women
TUESDAY Jan. 29, 2008 -- For some women, digital mammography is a better bet than traditional film mammography, a new study confirms.
Women under the age 50 with dense breasts who are premenopausal or perimenopausal get more accurate results with digital mammograms, said study author Dr. Etta Pisano, the Kenan professor of radiology and biomedical engineering at the University of North Carolina, in Chapel Hill.
Pisano was the principal investigator for a landmark study published in 2005, known as DMIST, that compared digital to film mammography for all women. In this latest research, Pisano decided to reanalyze the original findings by looking more closely at subgroups of women.
In the original study, 33 U.S. centers enrolled more than 49,000 women and determined the breast cancer status of more than 42,000. This latest research evaluated the mammograms of the 42,000 women. The new report was expected to be published in the February issue of Radiology.
The new analysis, said Pisano, "pretty much confirms what we found [in the original study]."
"In this latest study, we were trying to figure out which factor was most important," she said. To do that, they compared the accuracy results of digital versus film mammograms in 10 different subgroups of women, looking at combinations of the three factors -- menopausal status, age and breast density.
"And we couldn't figure out which factor was most important," Pisano said.
For other groups of women, no significant differences in accuracy were found between the two methods. The researchers did discover a trend toward improved accuracy of traditional film mammograms over digital ones for women over age 65 with fatty, rather than dense, breasts. However, the finding didn't reach statistical significance, Pisano noted.
Another expert, Dr. Carol H. Lee, chairwoman of the breast imaging commission of the American College of Radiology, agreed that the take-home message is for certain women to ask for digital mammograms.
"I don't think this [new study] says anything different than the original," Lee said. "They broke down the [original] subgroups into even more subgroups, They have 10 different ones. And they basically found that digital is very substantially better for pre- and perimenopausal women under age 50 with dense breasts."
Earlier this month, a study that appeared in the Annals of Internal Medicine crunched the same DMIST data and found that digital mammography was only cost-effective for this particular group of women.
In digital mammography, the X-ray film is replaced by "solid-state detectors that convert X-rays into electrical signals," according to the American College of Radiology. The detectors are akin to those found in digital cameras, and the electrical signals are used to produce breast images that can be viewed on a computer screen.
The denser the breast tissue, the more difficult it is to detect breast cancer on a mammogram, Lee explained. That's because dense tissue shows up as white on a mammogram and cancer shows up as white, too. "Fat shows up dark," she said. "So, cancer is easier to detect in fatty breasts."
If a mammogram report doesn't include information on breast density, Pisano suggested women ask their doctor or mammogram technician to provide that. Older women tend to have less dense breasts than younger women, but not always.
Digital mammography units aren't as plentiful in the United States as traditional units are, according to Arvind Gopalratnam, spokesman for GE HealthCare, a maker of digital mammography machines. About 20 percent of U.S. mammography units are digital; the other 80 percent are conventional.
The type of unit is only one factor playing a role in the accuracy of diagnosis, Lee added. The expertise of the technologist, as well as the skill of the radiologist who reads the mammogram, are also important, she said.
To learn more about mammography, visit the National Cancer Institute.
Posted: January 2008