Reporting Source: "For Some, Digital Mammogram Beats X Ray" NPR, Sept. 16, 2005;
"Digital vs Screening Mammography for Breast Cancer May Have Advantages." Medscape, Sept. 20, 2005;
"Digital Mammography Detects More Breast Cancers than Screen Film Mammography." Medical News Today, Sept. 17, 2005.
Primary Source : "Diagnostic Performance of Digital versus Film Mammography for Breast-Cancer Screening." The New England Journal of Medicine, Oct. 27, 2005; 353:1773-1783.
Expert Comments by Robyn Andersen, PhD, MPH
Fred Hutchinson Cancer Research Center, Seattle, WA
By Mary Batten
This is the largest study to compare the newer technology of digital mammography with traditional film mammography for screening women with no sign of breast cancer. More than 42,000 women from 33 centers in the United States and Canada underwent both screening procedures. Overall, no significant differences were found in the diagnostic accuracy of digital versus film mammography for most (40,553, or 94.8 percent,) of the women in this study. The greater accuracy of digital mammography was seen in 947 women (2.2 percent of the total study population) who comprised three subgroups: (1) those under 50 years of age, (2) those with dense breast tissue, and (3) premenopausal or perimenopausal women. Unfortunately, some media headlines, such as those mentioned in the reporting sources above, have given readers the impression that digital is better overall than film screening mammography. Only in the article that follows the headline does the reader learn that the women who gain an advantage from digital mammography are in one of the specified subgroups. The bigger story is the similarity between the accuracy of the two screening methods for most women. The results provide reassurance that film mammography, although not a perfect detection method, continues to be the gold standard screening procedure for most women (Ref. 1).
Many studies consistently show that screening mammography reduces the rate of death from breast cancer among women 40 years of age and older (Refs. 2-4). However, film mammography has well known limitations when screening women with dense breasts (Refs. 5-6). Premenopausal women are more likely to have dense breasts and when they develop breast cancer, it is a more aggressive disease. Thus it is essential to develop a test that can "see" through dense breast tissue. Digital mammography was developed to overcome some of the imaging limitations of film mammography.
Both digital and film mammography use x-rays to take pictures of the breasts but the resulting images are preserved differently. Film mammography uses film to capture, display and store the image. Digital mammography takes an electronic image of the breast and stores it directly in a computer, allowing the radiologist to increase the contrast in dense breast areas in order to obtain the best picture.
Previous smaller trials have not found digital mammography to be significantly more accurate than film mammography in diagnosing breast cancer (Refs. 7-11). The study reported here was large enough to detect small differences with statistical power.
What Was Being Studied?
The diagnostic accuracy of digital versus film screening mammography.
How Was Information Gathered?
The American College of Radiology Imaging Network conducted this trial, which is known as the Digital Mammographic Imaging Screening Trial (DMIST). Etta Pisano, MD, of the Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, led the study, which recruited more than 49,000 women over a two-year period. Women who came to the study sites for screening mammography were eligible to participate. None of the women had any symptoms of breast cancer. . After exclusions, a total of 42,760 women participated in the trial. All underwent both digital and film mammography in random order. Two radiologists independently read the mammograms. A biopsy or aspiration of any suspicious lesion was performed if either radiologist recommended it. A single pathologist or the study's principal investigator coded all pathological diagnoses on the basis of a review of tissue specimens or of the pathology report. All study participants were asked to come back in one year for a follow-up mammogram.
A total of 335 breast cancers were diagnosed. The diagnostic accuracy of digital and film mammography was similar for the study population as a whole. However, digital mammography was significantly better than film mammography in detecting breast cancer among women under age 50, those with dense breasts, and premenopausal or perimenopausal women. Digital mammography found 38 breast cancers, including many invasive and high-grade in situ cases that were missed by film mammography. All of these cases were found in women less than 50 years of age, premenopausal or perimenopausal women, and women with dense breasts. The researchers point out that these are the kinds of cancers that must be detected to save lives through screening.
Seventy-three breast cancers were missed by both digital and film mammography. These were also in women under 50 years of age, premenopausal or perimenopausal women, and those with dense breasts.
In addition to better diagnostic accuracy for young women, digital mammography has various other advantages:, say the researchers: (1) easier access to images and computer-assisted diagnosis; (2) improved means of transmission, retrieval, and storage of images; and (3) the use of a lower average dose of radiation without a compromise in diagnostic accuracy. They conclude: "We believe that the significant improvement in accuracy in specific subgroups of women justifies the use of digital mammography in these groups" (Ref. 1).
Who Funded This Study?
The National Cancer Institute
Overall, this is a nicely designed, well done study. It suggests that digital mammography is better for the women in these subgroups (under 50, dense breasts, pre- or perimenopausal) and that's really exciting because these are the subgroups for whom film mammography has not been as effective as it is for most women over the age of 50. So in some ways, it would encourage one to seek out digital mammography over regular film mammography. However, it wouldn't necessarily mean that if a new radiologist in town is doing digital part-time or on occasion, it would be better because he's using a different tool than somebody who is a real expert mammographer even if he was continuing to use film.
A lot of what goes on with mammography has to do not with the tool but with the person using the tool. That's one of the things we see in other studies. A lot of the differences in the performance of mammography have to do with whether the person who's reading the mammogram does it all the time and is very good at it or is somebody who reads them part-time or didn't receive as much training as someone else might have. Probably the first people to adopt digital mammography will only be the experts; in which case, the person who's doing digital mammography is the really good mammographer wherever you are.
We've had incredible difficulty documenting the value of mammography for women under the age of 50. We've got evidence for it now, which is really nice. This study is suggesting that a digital mammogram is a small but potentially significant improvement for exactly that group of women for whom mammography has always been questionable, for whom we've always been saying, we want it to work but we're not sure it's a good enough tool. It still may not be a great tool but it does suggest that there's improvement specifically for the people for whom we need it to be better.
This study is a further confirmation that for women over the age of 50, mammograms actually are a really quite good tool. Even for the women in the subgroups for whom digital was somewhat better, mammography still found most of the cancers. If there isn't a digital mammographer you can get to, don't give up on film. Digital may have a small marginal advantage and many women, for whom there is an option, are going to want to take advantage of that. But it doesn't mean that somebody should be really upset if it isn't an option for them because it's not a huge step forward. It's a small step forward but it's good to have every step.
Digital mammography is more expensive than film and it may take a while to get across the country but it's studies like this that would encourage people to upgrade their imaging technology. Now that there's some documentation that digital mammography works better for women under 50, there will probably be greater adoption of it in the near future.
Imaging works best to find things that are large and easy to see. Ideally we want to find the cancers before that, and people are doing their best to improve imaging technologies.
At the same time, people are also trying to find blood biomarkers that could be used for screening instead of visual imaging tools. The idea is that some cancers may excrete proteins into the bloodstream that we could use to identify a possible cancer before it can be seen. This would be a completely different mode of identifying who is at greatest risk, but at this point, there aren't any blood biomarkers on the immediate horizon.
1. Pisano ED, Gatsonis C, Hendrick E, et al. "Diagnostic Performance of Digital versus Film Mammography for Breast-Cancer Screening." The New England Journal of Medicine, Oct. 27, 2005; 353:1773-1783.
2. Humphrey LL, Helfane M, Chan BK, et al. "Breast cancer Screening: A Summary of the Evidence for the U.S. Preventive Services Task Force." Annals of Internal Medicine 2002; 137:347-60.
3. Institute of Medicine. S\Saving Women's Lives: Integration and Innovation: A Framework for Progress in Early Detection and Diagnosis of Breast Cancer. Washington, D.C.: National Academies Press, 2005.
4. Fletcher SW, Elmore JG. "Mammographic Screening for Breast Cancer." New England Journal of Medicine 2003; 348:1672-80.
5. Carney PA, Miglioretti DL, Yankaskas BC, et al. "Individual and Combined Effects of Age, Breast Density, and Hormone Replacement Therapy Use on the Accuracy of Screening Mammography." Annals of Internal Medicine 2003; 138:168-75.
6. Kerlikowske K, Grady D, Barclay J, et al. "Effect of Age, Breast Density, and Family History on the Sensitivity of First Screening Mammography." JAMA 1996; 276:33-8.
7. Cole E, Pisano ED, Brown M, et al. "Diagnostic Accuracy of Fischer Senoscan Digital Mammography versus Screen-Film Mammography in a Diagnostic Mammography Population." Academic Radiology 2004; 11:879-86.
8. Hendrick RE, Lewin JM, D'Orsi CJ, et al. "Non-inferiority Study of FFDM in an Enriched Diagnostic Cohort: Comparison with Screen-film Mammography in 625 Women." In: Yaffe MJ, ed. IWDM 2000: 5th International Workshop on Digital Mammography. Madison, Wis.: Medical Physics Publishing, 2001:475-82.
9. Lewin JM, D'Orsi CJ, Hendrick RE, et al. "Clinical Comparison of Full-field Digital Mammography and Screen-film Mammography for Detection of Breast Cancer." AJR American Journal of Roentgenology 2002; 179:671-7.
10. Skaane P, Young K, Skjennald A. "Population-based Mammography Screening: Comparison of Screen-Film and Full-Field Digital Mammography with Soft-copy Reading - Oslo I Study." Radiology 2003; 229:877-84.
11. Skaane P, Skjennald A. "Screen-film Mammography versus Full-Field Digital Mammography with Soft-copy Reading: Randomized Trial in a Population-based Screening Program - the Oslo II Study." Radiology 2004; 232:197-204.
Digital vs Film Mammography in the Digital Mammographic Imaging Screening Trial (DMIST): Questions and Answers, National Cancer Institute, Sept. 16, 2005
Digital Mammography Has Advantages in Breast Cancer Screening
Oncolink, Sept. 16, 2005
NBCC Reacts to ACRIN Release of Data of Digital Mammographic Imaging Screening Trial (DMIST)
National Breast Cancer Coalition, Sept. 2005
Are Mammograms Right for Everyone?
The New York Times, Nov. 1, 2005