Digital Mammography Outperforms Film for Some Women
Results from the largest randomized trial ever comparing digital mammography with standard film mammography confirm earlier indications that digital mammography is more accurate for women with dense breasts. Several other groups of women benefited from undergoing screening with digital mammography instead of film, including women under 50 and pre- and perimenopausal women.
Overall, 65 percent of trial participants fell into at least one of these groups.
"We found important breast cancers, the kind that kill women, using digital that we did not find with film, and the difference was significant in all three of those categories," said the study's principal investigator, Dr. Etta Pisano, of the University of North Carolina Department of Radiology. The study was not designed to determine whether there was a mortality benefit from digital compared with film. But, because film mammography has been shown to reduce breast cancer death rates, and digital proved to be more accurate for some women, Dr. Pisano said she "wouldn't be surprised" if it proved to save more lives in the long run.
The nearly 50,000-patient trial - the Digital Mammographic Imaging Screening Trial (DMIST) - was sponsored by the National Cancer Institute (NCI) and conducted by researchers in the American College of Radiology Imaging Network (ACRIN).
Consistent with several smaller trials, overall, the two screening methods performed equally in DMIST. But in the aforementioned subgroups, digital mammography provided a 15- to 28-percent accuracy advantage.
The study results were presented last Friday at an ACRIN meeting in Washington, D.C. - where Dr. Pisano spoke at a news conference - and published on the New England Journal of Medicine Web site.
Study participants underwent mammography by both methods and the results were interpreted independently by two radiologists. Breast cancer status was determined through available breast biopsy information within 15 months of study entry or through follow-up mammography at least 11 months after study entry.
An advantage of digital mammography for women with dense breasts makes sense, explains Dr. Mark Helvie, director of the breast imaging program at the University of Michigan Medical Center.
Dense breasts have a predominance of fibroglandular tissue, which absorbs a lot of x-ray beams and appears white on film. "These white areas can camouflage a cancer, which also looks white," Dr. Helvie says. Digital's superior resolution and image manipulation abilities can help unmask cancers embedded in dense breast tissue.
Although he voiced caution about interpreting too much from one trial, Dr. Helvie agreed that the results "suggest better detection [with digital] if you fall into one of these subsets." He added: "It looks like it's picking up tumors that you would want it to pick up."
Researchers are working on several improvements for digital machines, including ones "that could potentially allow for better spatial resolution," says Dr. Dan Sullivan, director of the NCI Cancer Imaging Program.
Dr. Pisano stressed that only 8 percent of the mammography machines in the United States are digital, meaning that not every woman who the DMIST data suggest should be screened digitally will have access to the technology. Other factors could affect access as well, including the higher cost of digital machines compared with film.
By Carmen Phillips