Digital vs. Film Mammography in the Digital Mammographic Imaging Screening Trial (DMIST): Questions and Answers
Key Points
- The study showed that digital mammography was significantly better that film mammography in screening women who were under age 50, or women of any age who had very dense breasts.
- Digital mammography allows improvement in image storage and transmission because images can be stored and sent electronically.
- Secondary goals measuring the relative cost-effectiveness of both digital and film technologies, and the effect on participant quality of life due to the expected reduction of false positives are still being assessed and will be reported at a later date.
- Death rates from breast cancer have been declining since 1990, and these decreases are believed to be the result, in part, or earlier detection and improved treatment.
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How is digital mammography different from film mammography?
Both digital and film mammography use X-rays to produce an image of the breast.
In film mammography, which has been used for over 35 years, the image is
created directly on a film. While standard film mammography is very good, it is
less sensitive for women who have dense breasts. Prior studies have suggested
that approximately 10 percent to 20 percent of breast cancers that were
detected by breast self-examination or physical examination are not visible on
film mammography. A major limitation of film mammography is the film itself.
Once a film mammogram is obtained, it cannot be significantly altered; if the
film is underexposed, for example, contrast is lost and cannot be regained.
Digital mammography takes an electronic image of the breast and stores it
directly in a computer. Digital mammography uses less radiation than film
mammography. Digital mammography allows improvement in image storage and
transmission because images can be stored and sent electronically. Radiologists
also can use software to help interpret digital mammograms. One of the
obstacles to greater use of digital mammography is its cost, with digital
systems currently costing approximately 1.5 to 4 times more than film systems.
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How was DMIST conducted?
The Digital Mammographic Imaging Screening Trial (DMIST), begun in October 2001,
enrolled 49,528 women, who had no signs of breast cancer, at 33 sites in the
United States. On the appointment day, women provided background health
information and filled out brief questionnaires. They also had both digital and
film mammograms taken on that day, each with a minimum of two views of each
breast. Two different certified radiologists interpreted the conventional and
digital mammogram exams for each individual patient. All radiologists who
participated read both types of mammograms, and each radiologist read
approximately an equal number of mammograms of each type.
Participants were asked to return in one year for their annual mammogram. At
that time, a mammogram was performed as part of routine health care. Women who
were not able to return to the same site as in year one were asked to submit
films from another institution for review by study radiologists.
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Why was DMIST important?
For women, breast cancer is the most common non-skin cancer and the second
leading cause of cancer-related death in the United States. Death rates from
breast cancer have been declining since 1990, and these decreases are believed
to be the result, in part, of earlier detection and improved treatment.
DMIST was performed to measure relatively small, but potentially clinically
important, differences in diagnostic accuracy between digital and film
mammography. While any differences that were detected might be relatively
small, they could improve breast cancer detection for all or some groups of
women.
Digital mammography is a newer technology that is becoming more common.
Currently, approximately 8 percent of breast imaging units provide digital
mammography. Past trials of digital mammography have shown no difference in
diagnostic accuracy between digital and film mammography. The U.S. Food and
Drug Administration (FDA) trials and three smaller screening trials showed no
significant difference in the performance of digital mammography vs. film
mammography. These studies were limited, however, because they each included
only one type of digital detector and had relatively small numbers of patients,
perhaps limiting their ability to detect small differences in diagnostic
accuracy.
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Who were the women who enrolled in DMIST?
Over 49,500 women who were requesting their usual breast cancer screening
mammogram were recruited at 33 sites in the United States and Canada. The women
had no breast cancer symptoms, and they agreed to undergo a follow-up mammogram
at the same participating site or provide their mammograms from another
institution for review one year from study entry. All women reviewed and signed
the study consent form.
The following women were ineligible:
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pregnant women
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women with breast implants
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women who had undergone a screening mammogram in the past 11 months
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women with a focal dominant lump, which is defined as a single lump felt by a
woman or her doctor
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women with a bloody or clear nipple discharge
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women with a history of breast cancer treated with lumpectomy
Breast cancer status for DMIST participants was determined through available
breast biopsy information within 15 months of study entry or through follow-up
mammography ten months or later after study entry.
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Who organized the study and how much did it cost?
The American College of Radiology Imaging Network (ACRIN) coordinated the
study. ACRIN is a Cooperative Group sponsored by the Division of Cancer
Treatment and Diagnosis at the National Cancer Institute (NCI). Enrollment
began in October 2001. On Nov. 14, 2003, DMIST reached its targeted 49,500
participant recruitment goal. ACRIN is a network of physicians,
scientists, and medical institutions that have joined together to conduct
clinical trials of new medical imaging technologies. The total cost of the
digital mammography trial was about $26 million.
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Which digital mammography equipment was included in DMIST?
General Electric Medical Systems, Fuji Medical Systems, Fischer Imaging, and
Hologic digital mammography systems were tested in the trial. Of these, all
except for the Fuji system are already FDA-approved and available for clinical
use in the United States.
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How important is reader training in interpreting digital mammography?
Breast cancer has a very similar appearance on digital and film mammograms, but
the display of the images on monitors instead of film requires additional
reader (radiologist) training. Under the federal law that governs mammography
in the U.S. (the Mammography Quality Standards Act), radiologists who switch
from interpreting film to interpreting digital mammography must undergo some
additional training.
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What were the main results of DMIST?
DMIST showed that, for the entire population of women studied, digital and film
mammography had very similar screening accuracy.
Digital mammography was significantly better in screening women who fit any of
these three categories:
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under age 50 (no matter what level of breast tissue density they had)
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of any age with heterogeneously (very dense) or extremely dense breasts
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pre- or perimenopausal women of any age (defined as women who had a last
menstrual period within 12 months of their mammograms)
There is no apparent benefit of digital over film mammography for women who fit
ALL of the following three categories:
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over age 50
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those who do not have dense or heterogeneously (very dense) breast tissue
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those who are not still menstruating
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.
These results suggest that for women who fall into three subgroups (women under
age 50, women with heterogeneously dense or extremely dense breasts, and pre-
and perimenopausal women), digital mammography may be better at detecting
breast cancer than traditional film mammography. Approximately 65 percent of
the women in DMIST fit into one of the three subsets that showed a benefit with
digital mammography.
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.
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How many of the study participants were diagnosed with cancer?
During the course of the study, including initial screening and follow-up, 335
women were diagnosed with cancer. In general, cancers detected by either film
or digital mammography were similar in histology (microscopic structure) and
stage (how advanced they were).
However, lesions detected by digital mammography and missed by film in women
under age 50, in women with heterogeneously dense or extremely dense breasts,
and in pre- and peri-menopausal women, included many invasive cancers and
medium and high grade in situ lesions. Many of these cancers were confined to
the breast at diagnosis; that is, they had not yet spread to the lymph nodes
under the arm. These are precisely the lesions that must be detected early to
save more lives through screening. In situ lesions in the breast are those
confined to the breast duct without invading the surrounding breast tissue and
are known as DCIS, or ductal carcinoma in situ.
Neither digital nor film mammography found all the breast cancers in the study
population. Women who develop lumps, breast changes, or symptoms after
screening mammography should report them to their physician even if their
mammogram showed no signs of breast cancer.
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Was the screening mammography performed in DMIST, both digital and film,
accurate?
Both digital and film mammography had sensitivities (the ability to tell if a
cancer is present) for breast cancer of 70 percent in the overall study
population using the conventional methods for measuring sensitivity in a breast
cancer screening trial.
The sensitivity for women with dense breasts was only 55 percent for film
mammography while the sensitivity for digital mammography was 70 percent. The
overall rate of 70 percent is within the expected rate of detection.
Specificities, or the ability to tell correctly that a cancer is NOT present
when the breasts are normal, were high for DMIST, just as would be expected of
screening mammography. Using one year follow-up interval, specificities for
both digital and film mammography were 92 percent for the overall population.
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Do the trial results suggest that women's lives will be saved if they undergo
digital mammograms and they are in one of the three groups that showed a
benefit with digital mammography?
DMIST was not designed to study breast cancer mortality, as that would have
been a much longer and more costly study. The improved diagnostic accuracy of
digital mammography in the subgroups of women found in DMIST may not translate
into saved lives. However, the types of lesions that were found by digital
mammography and not by film in these subgroups of the women were the types of
cancers that can lead to death -- that is, invasive cancers without evidence of
metastasis to axillary lymph nodes (lymph nodes under the arm and next to the
breast that is affected by cancer) at the time of diagnosis and medium and
high-grade in situ lesions (DCIS).
Randomized clinical trials that have studied mortality have shown a reduction
in mortality from breast cancer with the use of screening mammography, ranging
from 18 percent to 30 percent depending on the age of the women. DMIST results
indicate that screening with digital mammography will detect at least as many
breast cancers as film mammography over the whole population, and more advanced
or serious breast cancers in women in the three subsets of the population. This
suggests that at least as many -- and possibly more -- lives will be saved with
digital mammography as are now saved by screening with film mammography.
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Do the trial results indicate that ALL women should get digital mammograms instead of film mammograms for breast cancer screening?
No. The study results indicate that only women who fit in ANY of these three categories would benefit from digital mammography instead of film mammography:
- under age 50 (regardless of level of breast tissue density)
- of any age, with heterogeneously (very dense) or extremely dense breast tissue
- or pre- or perimenopausal women of any age (defined as women who had a last menstrual period within 12 months of their mammograms).
According to the results, women who fit ALL of the following three categories would not benefit from digital mammography instead of film mammography:
- over age 50
- those who do not have dense or heterogeneously (very dense) breast tissue
- and those who are no longer menstruating.
At present, only 8 percent of the mammography units in the United States have digital systems, whereas approximately 40 percent of women undergoing screening mammography have dense breasts. It will be impossible for all women who have dense breasts to receive digital mammograms, at least for the near future. As more digital mammography systems become available, more women in the groups who are likely to benefit from digital mammography will have access to this technology.
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What were the secondary goals of this trial and what were those results?
Secondary goals included:
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measurement of the relative cost-effectiveness of both digital and film
technologies, as digital mammography costs 1.5 to 4 times more than film
mammography
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the measurement of the effect on participant quality of life due to the
expected reduction of false positives
The results of these parts of the study are still under analysis and will be
presented at a later date. In fact, even though a reduction in false positives
with digital mammography was expected, none was found in DMIST. The effect of
false positive results on quality of life will be reported at a later date.
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Reader (radiologist) studies also were conducted using the mammograms obtained
in DMIST. What were the studies and what were the results?
Seven controlled reader studies were used to measure the following:
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diagnostic accuracy of softcopy (displayed on a computer monitor) vs. printed
film display for digital mammography
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effect of disease prevalence (percent of trial participants who actually had
breast cancer) on reader interpretation performance
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effect of breast density on the diagnostic accuracy of digital mammography vs.
film mammography
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diagnostic accuracy of each of the four individual digital mammography units
vs. film mammography
The analysis of the reader studies has not been completed at this time.
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What does NCI recommend for screening mammograms?
NCI recommends that:
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Women in their 40s should be screened every one to two years with mammography
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Women aged 50 and older should be screened every one to two years
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Women who are at higher than average risk of breast cancer should seek expert
medical advice about whether they should begin screening before age 40 and the
frequency of screening
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How can women obtain digital mammograms?
Film mammography is still much more common that digital mammography. Women who
would like to have digital mammograms can ask their doctors or contact local
hospitals or imaging centers to find out if digital mammography is available in
their area.
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Should women who live in communities that don't have digital mammography
facilities, or don't have enough available machines, delay their next
mammograms until they can have digital mammograms? Should women in the affected
categories try to get digital mammograms before they are scheduled for their
next mammogram?
Women should have their next mammogram when they are scheduled for it. It would
be better to have a film mammogram when a woman is supposed to have her next
mammogram than for her to delay her screening in order to get a digital
mammogram. Women should not defer screening with mammography just because of a
lack of access to digital mammography. Film mammography has been successfully
used as a screening tool for breast cancer for over 35 years.
Women should not receive an extra mammogram because of these trial results.
That is, if a woman has had a mammogram in the last year, and she has no breast
signs or symptoms, she should undergo her next screening mammogram only when
she is due for one, not earlier than she would ordinarily be scheduled.
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What should women do who have larger, dense breasts that require multiple
digital exposures to obtain an accurate view of a portion of the breast instead
of one larger image for each view? Is additional dose an issue?
Only the GE FDA-approved digital mammography system provides an imaging area
that is smaller than that used for the usual film mammogram. This means that
some women with large breasts will require extra images with digital
mammography instead of only two images of each breast with film mammography.
In the DMIST study, 19 percent of all participants required one or more extra
views with digital mammography over and above what was required with film
mammography in order to include all portions of their breasts. About 25 percent
of those women scanned with the GE system, however, required more images with
digital mammography than they did for their film mammograms. The women who
required the extra images who have dense breasts are typically the women for
whom digital mammography was shown to be more accurate than film.
In considering this issue, it is important to realize that increasing the
number of images per view does not dramatically increase the dose because not
all breast tissue is exposed in each view. For example, taking two digital
images of the breast instead of one film mammogram does not double the dose
overall, because only a portion of the breast is exposed twice. On average, the
larger number of digital images required is more than offset by the lower doses
delivered by digital mammography for women with thicker and denser breasts.
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How does a postmenopausal woman over age 50 determine if she has extremely dense
or heterogeneously dense breasts?
At present, this can only be determined by a prior mammogram. Usually the
density rating on mammography should be noted in the written report from the
interpreting radiologist who reads the mammogram. If it is not included in the
mammography report, it can be determined by a radiologist or qualified
mammography technologist by viewing a prior mammogram. Women who are uncertain
about their density status should inquire about it at the time of their next
mammography visit.
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If a woman has dense breasts, will she have dense breasts for the rest of her
life?
Breast density can change over time. Most frequently, breast tissue becomes
less dense with age. Estrogen replacement therapy, menopause, and weight loss
or gain can change a woman's breast density. If a woman has questions about her
breast density, she can discuss it with her primary care physician or the staff
at the clinic where she receives her mammograms.
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Does getting a digital mammogram feel similar to getting a film mammogram?
From a woman's perspective, a digital mammography examination is similar to a
traditional mammography examination. Positioning and compression of the breast
are identical.
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What other breast imaging techniques might be useful for breast cancer
screening?
In addition to mammography, ultrasound and magnetic resonance imaging (MRI) are
both sometimes used to screen for breast cancer. ACRIN is currently conducting
another trial of breast cancer screening, which compares ultrasound vs.
mammography in high- risk women. MRI has shown promise for women at high-risk
for breast cancer. DMIST did not study either of these other technologies. In
fact, women who participated in DMIST were not permitted to participate in
other screening trials during the one year immediately before and after their
entry into DMIST.
There are no multicenter clinical trials investigating the use of either MRI or
ultrasound in place of mammography as screening tools for breast cancer for the
general population of women over age 40.
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Are there other possible advantages of digital mammography over film
mammography?
Digital mammography offers 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.
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What levels of radiation are used for digital mammography vs. film mammography?
In DMIST, digital mammograms required approximately three quarters the
radiation dose of film mammography. However, the dose in film mammography is
quite low and poses no significant danger to patients.
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How many women are screened with mammography annually in the United States?
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 (to detect cancer as opposed to following cancer once it has been
diagnosed). This translates to about 23.5 million screening procedures every
year.
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What are the costs of different types of mammograms?
Reimbursement by Medicare in 2005 for film-screen mammograms is $85.65 and for
digital screening mammography (for women with two breasts, as opposed to those
who have undergone mastectomy) is $135.29. Actual cost for mammograms will vary
by region and the form of reimbursement.
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What is telemammography?
Telemammography is the transmission of digital mammograms electronically so
that they might be interpreted in a remote location. This can be accomplished
through wireless networks (such as through satellites) or through more
traditional wire-based networks. This may allow access to experts and second
opinions more quickly for digital mammograms, particularly for women in
underserved areas. Of course, second opinions are also available with film
mammography by shipping mammograms using mail and other delivery services.
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Who were the investigators who conducted the study?
The study was led by Etta D. Pisano, M.D., of the Department of Radiology and
Biomedical Engineering, the Biomedical Research Imaging Center and the
Lineberger Comprehensive Cancer Center of the University of North Carolina at
Chapel Hill.
Edward Hendrick, Ph.D., with the Department of Radiology, Northwestern
University, Chicago, Ill., was co-principal investigator of the study. Martin
Yaffe, Ph.D., Department of Imaging Research and Medical Imaging of the
University of Toronto, Toronto, Ontario, Canada, was the lead physicist. The
Center for Statistical Sciences at Brown University, Providence, R.I., provided
statistical coordination for the study under the direction of Constantine
Gatsonis, Ph.D. Dennis Fryback, Ph.D., at the University of Wisconsin at
Madison, directed the health-related quality of life analysis and Anna
Tosteson, Sc.D., at Dartmouth Medical School, Hanover, N.H., directed the
cost-effectiveness evaluation. Data/Image collection and study coordination was
performed at the American College of Radiology, ACRIN headquarters, located in
Philadelphia, Pa.
The citation for the online publication of the study results in the New England
Journal of Medicine is: Pisano E, Gatsonis C, Hendrick E, Yaffe M, Baum J,
Acharyya S, Conant E, Fajardo L, Bassett L, D'Orsi C, Jong R, and Rebner M.
Diagnostic Performance of Digital versus Film Mammography for Breast Cancer
Screening - The Results of the American College of Radiology Imaging Network (ACRIN) Digital Mammographic Imaging Screening Trial
(DMIST). NEJM, published online September 15, 2005 and in print on October 27,
2005.
For a list of institutions that participated in the study and contact
information, please go to http://www.dmist.org.
# # #
For a press release about this study, please go to
http://www.nci.nih.gov/newscenter/pressreleases/DMISTrelease.
For more information about cancer, visit the NCI Web site at http://www.cancer.gov
or call NCI's Cancer Information Service at 1-800-4 CANCER (1-800-422-6237).
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