Is Mammography Going Digital?
Just as the use of digital cameras is rapidly catching up to that of traditional film photographs, so too may digital mammography and computer-aided detection of breast lesions soon surpass traditional film mammography as the preferred screening tool for breast cancer.
But not yet.
At the recent annual meeting of the Radiological Society of North America in Chicago, promising early results were presented on two new mammography technologies: computer-aided detection (CAD) and digital mammography (DM). If preliminary clinical trial results are any indication, both of these techniques could someday result in faster interpretations, more accurate readings, and earlier detection of even the smallest tumors.
In the first presentation, researchers led by Dr. Timothy Free compared screening results using both mammography and computer-aided detection (CAD) in a clinical trial of 12,860 women conducted at the Women's Diagnostic & Breast Health Center in Plano, Texas.
CAD scans digital images of the mammogram and marks areas on the image where the computer finds a pattern suggestive of early cancer.
A total of 49 unsuspected cancers were detected during the study period: 32 by both CAD and the radiologist (using a traditional mammogram); 9 by the radiologist alone, and 8 by CAD alone. The use of CAD in the interpretation of the mammogram increased the number of cancer detected by 20 percent. Importantly, all 8 of these additional cancers were in very early stages, when they are most easily treated.
In a second study presented at the conference, researchers from the University of Colorado and the University of Massachusetts screened 6,768 women with both digital mammograms (DM) and conventional film mammograms. Of the women studied, 183 were found to have a suspicious abnormality leading to a biopsy, which confirmed that 51 of those were 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 neither CAD or DM have so far proven to be better than film mammography in detecting cancers, they are clearly emerging technologies that are certain to improve rapidly. Their likely advantages include:
The Food and Drug Administration recently gave its approval to a new Computed Tomography (CT) system made by Siemens Corp., which will enable oncologists to receive more accurate information on the size, shape, location and condition of tumors. Also, because the new CT scanner moves along a set of rails encircling a treatment table, the results can be immediately applied to a patient's care.
The FDA earlier gave its approval to a General Electric digital mammography system, which it cited as an improvement over the standard film images now used by most radiologists. The digital technology allows doctors to store and transfer images electronically, and 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. The new techniques becoming available can locate much smaller tumors, especially in dense breast tissue. They can 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.
It's about time. There have literally been thousands of press stories in recent years regarding the controversy of mammography screening for women. Many have centered on their effectiveness for younger women, especially their cost versus benefit. And recently, the debate was inflamed even further when the medical journal The Lancet published an article by a pair of Danish researchers concluding that the benefits from mammography screening were "weak" in terms of reduced mortality.
That article incited a huge international outcry from physicians concerned that the publicity generated from this dissenting study could undermine worldwide mammography screening programs-still the most common way to detect breast cancer other than breast self exam.
In a swarm of follow up letters to The Lancet, outraged physicians said the publicity from the report could erode public confidence in mammography screening programs and undermine well-researched conclusions about their efficacy.
Interestingly, one aspect of mammography accuracy that has received relatively little attention is the actual skill of the physician interpreting the mammograms.
Dr. Wendie Berg and colleagues in the Department of Radiology at the University of Maryland Medical Center have studied this issue and developed a pilot course to train radiologists in better mammography interpretation.
Berg's zeal for improving mammography reading came as the result of a shocking discovery. She took the same mammogram film to five well-respected mammographers in Baltimore and came away with a wide variety of interpretations and recommended courses of treatment.
Since mammography is still the most widespread screening method for breast cancer, Berg was alarmed. She immediately began working on an educational program for radiologists that would provide a standard approach for interpreting mammograms. The result was a course for radiologists which teaches a mammography reading system using the standardized Breast Imaging Reporting and Database (BI-RADS) terminology developed through the American College of Radiology. It provides a more efficient model for catching cancerous lesions and interpreting results.
"Early detection is by far the most important factor in successfully treating breast cancer," said Berg. "And the more accurate a radiologist reads a mammogram, the sooner treatment can commence."
New radiographic technology in the years to come is certain to have a huge impact on locating breast cancer tumors at their earliest-and most treatable-stages. However, in the interim, advances in something as low-tech as the improved reading a mammogram may be just as revolutionary.
SOURCES:
Abstracts from the 86th Scientific Assembly and Annual Meeting of the Radiological Society of North America, November 29, 2000, Chicago, Illinois
Abstracts from the 22nd Annual San Antonio Breast Cancer Symposium, Dec. 8-11, 1999, San Antonio, Texas
Abstracts from the 17th Annual Miami Breast Cancer Conference, Mar. 6-7, 2000, Miami, Florida
U.S. Food and Drug Administration (http://www.fda.gov)
The Lancet, Jan. 8, 2000; Vol. 9198
The Lancet, Feb. 26, 2000; Vol. 9205
Symposium on Applying BI-RADS to Mammography Practice, Sept. 26, 1999, Baltimore, Maryland
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