The much-anticipated results of the Digital Mammography Imaging Screening Trial (DMIST) are out - revealing that digital mammograms are better than analog x-rays in detecting breast cancer in younger women and those with dense breasts. But for the majority of the population, there is no difference in detection using analog or digital mammography, the landmark study concluded.
The largest study of its kind ever conducted involved 42,760 asymptomatic women who were imaged at 33 sites across the U.S. and Canada since October 2001. Women in the trial were given both digital and film exams, which were interpreted by two different radiologists. Breast cancer status was determined through available breast biopsy information within 15 months of study entry or through follow-up mammography 10 months or later after study entry.
The study, sponsored by the National Cancer Institute (NCI), was published online Thursday by the New England Journal of Medicine, which will publish it in the Oct. 27 edition. The results also were announced Thursday at a meeting of the American College of Radiology Imaging Network in Pentagon City, Va.
"These results will give clinicians better guidance and greater choice in deciding which women would benefit most from various forms of mammography," said senior author, Etta Pisano, MD, of the University of North Carolina at Chapel Hill.
"There is now general agreement that screening mammography reduces the rate of breast cancer among women who are 40 years of age or older," the report in the NEJM begins. "Meta-analyses of eight large, randomized trials found a reduction in the mortality rate of 16 to 35 percent among women 50 to 69 years of age who were assigned the screening mammography, whereas women who were 40 to 49 years of age at entry had a smaller but significant reduction of 15 to 20 percent."
The study showed that digital mammography detected up to 28 percent more cancers than standard mammograms in younger women and those with dense breasts. A total of 335 breast cancers were found. Both types of mammograms missed about 30 percent of them.
Digital mammograms proved 15 percent more accurate than standard film X-rays among women under 50, in whom breast cancer is relatively uncommon. Among women with dense breasts and those not yet in menopause, digital mammograms were 11 percent and 15 percent better, respectively.
The study also points out that digital mammograms offer other advantages over film, including "improved ease of image access, transmission, retrieval and storage, and lower average radiation dose without a compromise in diagnostic accuracy. In addition, digital mammograms are less likely than film mammograms to be lost," NCI said. Also, NCI pointed out that the digital mammograms required approximately three quarters the radiation dose of film mammography. However, they continued, "the dose in film mammography is quite low and poses no significant danger to patients."
In addition, there was no statistically significant difference in the accuracy of digital mammography compared to film according to digital mammography machine type, race, or breast cancer risk.
Some earlier studies had suggested that digital mammography would result in fewer false positives than film mammography, but the rates of false positives for digital mammography and traditional mammography were the same in DMIST.
The FDA reports that there are about 33.5 million mammography procedures performed per year in the United States. Data from 2000-2002 show that about 70 percent of all mammograms that are performed annually are for screening purposes. This translates to about 23.5 million screening procedures every year.
NCI estimates that only 8 percent of mammography equipment today is digital, largely attributed to cost - with a digital mammography system selling 1.5 to 4 times more, with price tags for digital mammography units ranging from $400,000 to $500,000 vs. $75,000 to $125,000 for an analog unit. There also is the consideration for viewing and archiving digital mammograms. Medicare pays an average of $85.65 for a standard film mammogram and $135.29 for a digital one.
The vendors whose digital mammography systems were used in the trial include: GE Healthcare, Fuji Medical Systems, Fischer Imaging and Hologic. The Fuji system is not yet approved for use in the U.S.
Results that measure the cost-effectiveness of digital and film technologies and the effect on participant quality