Report from RSNA: DMIST results highlight possible downsides of digital mammography in older women

November 27, 2006

New analyses of data from the Digital Mammographic Imaging Screening Trial show that digital mammography is superior only for pre- and perimenopausal women with dense breasts. Screen-film mammography may actually have an edge in older women with fatty breasts, according to a study presented at the RSNA meeting on Sunday.

New analyses of data from the Digital Mammographic Imaging Screening Trial show that digital mammography is superior only for pre- and perimenopausal women with dense breasts. Screen-film mammography may actually have an edge in older women with fatty breasts, according to a study presented at the RSNA meeting on Sunday.

Screen-film mammography may actually have an edge over digital mammography in certain populations, according to Dr. Etta Pisano, principal investigator of the Digital Mammographic Imaging Screening Trial, who gave a presentation on Sunday.

"We believe improved contrast in digital mammography is likely to be the factor that allows for improved performance," said Dr. Etta Pisano, chief of breast imaging at the University of North Carolina, who presented results. "My own hypothesis is that contrast for digital mammography is optimized for dense breasts and not yet optimized for fatty breasts."

An analysis of Medicare reimbursement rates in a related study presented at the same session found that digital mammography is not cost-effective for screening of the general population of mammography-eligible women.

DMIST results released last year showed the benefits of digital mammography for younger women, but the reasons behind improved performance were unclear. At the time, questions arose over why digital screening did not confer benefits for the population overall and whether performance might be lower in some subgroups.

Pisano said researchers have now analyzed subgroups of women in the DMIST by age, menopausal status, and breast density. The overall trial enrolled 50,000 women.

The researchers found no statistically significant differences between digital and screen-film mammography except for pre- and perimenopausal women with dense breasts who were under 50. For these women, digital mammography's improved sensitivity over screen-film mammography did not come at the expense of specificity.

Screen-film mammography was more sensitive in women over 65 with fatty breasts, but the difference was not statistically significant. Still, the data could indicate a slight trend toward better performance of conventional mammography in older women with fatty breasts, according to Pisano.

Providers imaging women with fatty breasts on digital systems may want to be aware of this possible difference and spend more time on these cases, she said.

DMIST analyses also indicate that performance varied depending on the type of machine used. In cases where Fischer equipment was used, more cancers were missed than with other machines.

Readers' varying abilities may explain differences in performance of digital versus screen-film mammography, but a full analysis of interpretation skills in DMIST will not be available for some months. A retrospective study of 320 asymptomatic cases, however, found no difference in accuracy between digital and screen-film mammography. These results were also presented at the RSNA meeting.

It is unclear why these results seem to contradict the DMIST findings, but they could be due to the fact that prior films and clinical information were not made available to readers. Or readers may perform differently in the study environment as opposed to clinical practice.

Digital mammography needs to promise better performance to pay its way. The technology costs significantly more than conventional equipment, and providers would need higher reimbursement for the technology to be cost-effective. DMIST researchers analyzed cost-effectiveness for women of various ages and breast densities, based on Medicare reimbursement, costs for treatment, and effects on quality of life and mortality rates.

Digital mammography was cost-effective if used in a targeted fashion for younger women with dense breasts. It helped to increase the number of cancers detected at the time of screening, while cutting mortality rates.

But the case for screening all women was not borne out. In fact, screening all women with digital technology was more expensive and less effective than using digital mammography in a targeted way, said Dr. Anna Tosteson, a professor of medicine at Dartmouth-Hitchcock Medical Center.

"Digital screening for all women does not provide sufficient health gains to warrant increased costs," she said.

For more online information, visit Diagnostic Imaging's RSNA Webcast.