FDA Cautious About Digital Mammograms

The U.S. Food and Drug Administration has just issued guidelines that will temporarily limit the number of mammography facilities which are authorized to perform digital mammography.

Digital mammography is a new breast cancer screening technique that uses computerized digital images to scan the breast for abnormalities. Traditional mammography is based on taking film images of the breast.

The FDA decided to limit the number of digital mammography systems until it can develop a way to standardize quality assurance procedures, similar to those in place for standard film mammography as a result of the Mammography Quality Standards Act (MQSA).

In 1992 Congress enacted the MQSA to ensure that all women have equal access to quality mammography for the detection of breast cancer in its earliest, most treatable stages. In 1998, Congress reauthorized the MQSA, extending the program to 2002.

As part of the MQSA legislation, Congress charged the Food and Drug Administration with developing and implementing regulations to help ensure that mammography is consistently safe and reliable, and that consumers receive uniformly high-quality services from facilities throughout the United States.

The FDA is following a similar approach in developing guidelines for digital mammography. But until it completes this task, the agency is only authorizing digital mammography to be performed in facilities that are already accredited to perform analog mammographies.

Promising Technology

Just as the use of digital cameras is rapidly catching up to that of traditional film photographs, so too may digital mammography soon surpass traditional film mammography as the preferred screening tool for breast cancer.

At the recent annual meeting of the Radiological Society of North America in Chicago, promising early results were presented on a number of new mammography technologies, including digital mammography (DM). If preliminary clinical trial results are any indication, digital mammography could soon result in faster interpretations, more accurate readings, and earlier detection of even the smallest tumors.

In a study presented at the conference, researchers from the University of Colorado and the University of Massachusetts screened 6,768 women with both digital mammograms and conventional film mammograms. Of the women studied, 183 were found to have a suspicious abnormality leading to a biopsy, which eventually confirmed that 51 of these abnormalities were indeed cancers.

Eighteen of these cancers were detected on both digital and film mammography. DM alone detected 9 cancers missed by film mammography; film mammography detected 16 missed by DM; and 8 were missed by both methods. (These cancers were diagnosed when they became noticeable in subsequent months.)

While digital mammography has therefore not yet been proven superior to film mammography in detecting cancers, there are clearly some significant potential advantages if the technique can be perfected:

• Faster exams. A DM image is available in about 10 seconds vs. 2 minutes for a conventional film mammogram, which must be developed.
• Better contrast resolution. DM is able to distinguish more shades of gray than can film mammography. This may prove to be an advantage in detecting cancers surrounded by dense normal tissue.
• Easy retrieval. Because DM images are computerized, they are faster and easier to retrieve, and are unlikely to be lost, as can happen with films. Radiologists also will be able to share digital images via computer hook-ups, so breast-imaging experts can examine images taken at other locations.
• Easy correction. Radiologists will be able to manipulate images to correct for under- or over-exposure, possibly saving women from the need for another mammogram when initial results seem inconclusive.

The technology of mammography is changing rapidly-and for the better. New techniques such as digital mammography will soon be able to locate much smaller tumors, especially in dense breast tissue. They should also more accurately determine whether the tumors are cancerous or not, thus avoiding the need for biopsies and other clinical procedures.

Furthermore, many of these new technologies are taking much of the human guesswork out of the process. The possibility of diagnostic error by a radiologist is being minimized by increasingly detailed images from computers and machines.

SOURCES:
Abstracts from the 86th Scientific Assembly and Annual Meeting of the Radiological Society of North America, November 29, 2000, Chicago, Illinois
"Premarket Applications for Digital Mammography Systems; Final Guidance for Industry and FDA," U.S. Food and Drug Administration, February 16, 2001 (http://www.fda.gov/cdrh/ode/guidance/983.pdf)

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