A large, head-to-head comparison of digital and film mammography found no overall difference in diagnostic accuracy, but digital mammography appears to have better diagnostic accuracy in some subgroups of women.
Digital mammography was significantly more accurate among women aged under 50 years, women with heterogeneously dense or extremely dense breasts, and premenopausal or perimenopausal women, according to the study by Etta D. Pisano, M.D., of the University of North Carolina at Chapel Hill, and colleagues.
The study involved a total of 49,528 women recruited over a 2-year period at 33 sites in North America. The final analysis included data from 42,760 women for whom the investigators had all relevant information (N. Engl. J. Med. 2005;353:[Epub ahead of print] doi 10.1056/NEJMoa052911, www.nejm.org
All women underwent both digital and film mammography, and these were independently interpreted by two readers. Readers rated the mammograms on a seven-point malignancy scale and used the classification of the Breast Imaging Reporting and Data System (BIRADS).
Biopsy or aspiration of the suspicious lesion was performed if either reader recommended it. These patients received follow-up mammograms an average of 455 days following their initial screening. A total of 335 cancers were detected among the women enrolled in the study.
Investigators used five digital mammography systems from four manufacturers. No statistically significant differences were found among the different mammography systems.
The investigators noted that the cancers detected by digital mammography but missed by film mammography included many invasive and high-grade in situ cases, precisely the lesions that must be detected to save lives.
The study found no advantage in the diagnostic accuracy of digital mammography for women aged 50 years and older, women with fatty breasts or scattered fibroglandular densities, and postmenopausal women.
But digital mammography has other advantages, the investigators noted. These include easier access to images and to computer-assisted diagnosis; improved means of image transmission, storage, and retrieval; and the use of a lower average dose of radiation without compromising diagnostic accuracy.
Conversely, the cost of digital mammography systems, which the investigators place at 1.5–4 times higher than film systems, provides a barrier to the universal use of this modality.