Sticking with Mammograms ... For Now
In 1999, the Institute of Medicine (IOM), a branch of the National Academy of Sciences, established a committee to examine current technologies for the early detection of breast cancer. After two years of study, the IOM has just released its findings: Mammograms are still the best tool available for breast cancer screening.
"Although many of the newer tools offer certain advantages and deserve to be studied further, film mammography remains the gold standard for screening," said Dr. Joyce Lashof from the University of California, Berkeley, who chaired the IOM review committee.
Several new technologies on the horizon show promise, the report concluded, but none have yet proven superior to traditional x-ray film mammography in screening for breast cancer. In fact, no single imaging technology-including mammography-is capable of accurately detecting all breast abnormalities.
"Ultimately," the report said, "the best detection may come from using several different tools."
For example, the report specifically highlighted ultrasound and magnetic resonance imaging (MRI), which have shown significant diagnostic potential when used in conjunction with mammography, especially in getting a clearer picture of dense breast tissue in younger women.
In presenting the findings of the Institute of Medicine report, Lashof acknowledged that screening mammography cannot detect all cancers, including some that are found by physical examination. Mammograms are particularly difficult to interpret for women with dense breast tissue, she said, which is especially common in younger women.
"Dense tissue interferes with the identification of abnormalities associated with tumors," Lashof noted, "leading to a higher rate of false test results among these women." As many as three-quarters of all breast lesions that are biopsied because of suspicious findings on a mammogram eventually turn out to be benign (non-cancerous).
Therefore, Lashof said, because of the prevalence of breast cancer and the inherent limitations of mammography, we need to intensify our search for more effective technologies for early detection. These include digital mammography, ultrasound, computer-aided detection systems, and magnetic resonance imaging (MRI).
Digital mammography uses computerized digital images to scan the breast for abnormalities. It offers better contrast resolution than a traditional film mammogram, and digital images can be stored on computer files and sent to other radiologists for consulting opinions.
Breast ultrasound sends high-frequency sound waves through the breast, which are then picked up and translated by a computer into a computer image. Ultrasound can detect the increased blood flow common to cancers and can distinguish between cancerous and noncancerous cysts. It can also be used to help doctors precisely guide a biopsy needle into breast lesions.
Computer-aided detection systems scan digital images of the mammogram that can be displayed on a computer screen. They mark areas on the image where the computer finds a pattern suggestive of early cancer.
Magnetic resonance imaging uses a large magnet and radio waves to measure the electromagnetic signals your body naturally gives off. It makes precise images of the inside of the body, including tissue and fluids.
While improvements in breast imaging technology are progressing rapidly, the Institute of Medicine report cautioned that our understanding of the basic biology of breast cancer still has a long way to go. For example, better imaging has led to the detection of smaller, early lesions, such as ductal carcinoma in situ, the biology of which is not well understood.
"Currently, the methods for classification of such lesions detected by mammography are based on the appearance of the tissue structure, and the ability to determine their lethal potential is crude at best," the report emphasized.
The report called for additional research funding to better understand the progression of breast cancer, to more clearly define the significance of early lesions, and to develop reliable biomarkers to gauge the risk of breast cancer development.
Finally, the IOM committee sounded a warning signal about the lack of access to adequate screening facilities for many women, particularly minorities. It also called on the Health Care Financing Administration and a panel of independent experts to analyze the current Medicare and Medicaid reimbursement rates for mammography to determine whether the cost is adequately covered.
The report further called on the National Cancer Institute to sponsor long-overdue studies on the benefits of screening mammography for women over the age of 70, which has been difficult to assess because of a lack of participation by older women in clinical trials. But as the age distribution of the U.S. population continues to shift toward older ages, it warned, the question of whether these women can benefit from screening mammography will be come increasingly important.
SOURCE:
"Mammography and Beyond: Developing Technologies for the Early Detection of Breast Cancer," Institute of Medicine National Research Council, National Academy of Sciences, March 8, 2001 (http://www.nas.edu)
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