Digital mammograms are 15% to 28% more effective than those using film at detecting breast tumors in women under 50, those with dense breast tissue and women entering menopause, according to a landmark study comparing the techniques.
Those three groups, which substantially overlap, account for about 55% of all U.S. women. Women in those groups are more likely to have fast-growing, aggressive tumors for which early detection and treatment are crucial for a cure.
"These are cancers that kill women and [many] were missed on film," said Dr. Etta Pisano of the University of North Carolina at Chapel Hill, who led the study of about 50,000 women.
Wider use of digital imaging, which accounts for about 8% of all mammograms, "should save more lives," she said.
"There is no question in my mind that this will be the mammography of the future," said Dr. Lawrence Bassett, a breast-imaging expert at UCLA's Jonsson Comprehensive Cancer Center.
Mammography is the most common and effective way of detecting breast tumors, which affect an estimated 211,000 American women each year, killing 40,000.
Conventional mammograms detect about 70% of tumors in older women, but about 55% in younger women and those with dense breast tissue.
As women age, their breasts generally acquire a higher proportion of less-dense, fatty tissue that allows for easier detection of tumors.
Pisano presented the results Friday at a meeting of the American College of Radiology Imaging Network in Arlington, Va., and they were published online the same day by the New England Journal of Medicine.
For the remaining 45% of women, primarily post-menopausal women, digital mammography was about as effective as the conventional form, the study found.
But Dr. Yuri Parisky, the senior mammographer for the USC School of Medicine, said he believed that digital imaging could prove to be more effective for post-menopausal women as well.
He pointed out that the study was performed with first-generation digital equipment, saying, "The advances since this study have been pretty profound."
Improvements have been made in software, digital detectors for recording X-rays, workstations for displaying data and three-dimensional imaging.
"I wish I could afford to have all my units replaced with digital mammography," Parisky said.
Digital mammography presents other advantages as well, according to experts such as Dr. Phil Evans of the University of Texas Southwestern Center for Breast Care in Dallas.
Digital images can be enhanced by changing contrasts and magnified to view isolated areas. They require less radiation and are easier to produce, store and transmit, Evans said.
"In terms of ease, convenience and throughput, [digital mammograms] are starting to make sense economically," Parisky said. "This study makes the medical justification for them."
The $26-million study was organized by the American College of Radiology and funded by the National Cancer Institute. Physicians at 33 sites around the country enrolled 49,528 women with no symptoms of breast cancer.
Each woman received a conventional film mammogram and a digital mammogram, which were read by separate teams of investigators. The women were followed for about 18 months, during which 335 were diagnosed with breast cancer.
Overall, the two techniques were roughly comparable in their ability to detect tumors, but there were major differences in the three subgroups of women.
Among those under 50, conventional mammography missed about a third of the tumors detected digitally. Among women with dense breasts, film mammography missed about a quarter of the tumors. And among women who had just entered menopause or who entered it soon after joining the study, film missed as many as 40% of the tumors.
"That was the major surprise of the study," Evans said. "These subsets of women have a pretty dramatic benefit from digital mammography."
The primary drawback to the technique is cost. Digital equipment costs as much as $500,000, about three to four times as much as conventional film equipment.
Digital mammograms are generally about 50% more expensive than those on film, costing about $135 compared with about $86 for film.
"Many people have been waiting on this study" to see if the improvement would be large enough to justify the increased cost, Evans said.
The study indicates that the cost probably is justified if the screening is targeted toward the three groups, said Robert A. Smith, the American Cancer Society's director of cancer screening.
But if digital mammography is not available to them, he emphasized, "it should be remembered that traditional film mammography is also effective."
(BEGIN TEXT OF INFOBOX)
Digital mammograms are more effective than standard X-rays at detecting breast cancer in young women and those with dense breasts, but not for most post-menopausal women, according to a landmark study.
Medicare procedures, 2003
Standard X-ray film: 5,136,722
Medicare reimbursement, national average
Standard X-ray film: $85.65
Total number of screening mammograms, estimate
Digital: 1 million
Standard X-ray film: 22.5 mil.
Los Angeles Times