Using MRI and Ultrasound to Detect Breast Cancer
Two presentations at the recent Miami Breast Cancer Conference focused on the benefits that magnetic resonance imaging (MRI) can have in breast cancer screening and detection.
A magnetic resonance imaging machine 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.
In the first presentation, Dr. Steven Harms of the University of Arkansas for Medical Sciences in Little Rock reported that using MRI to screen young women who are at high risk for breast cancer may actually be superior to mammography.
He noted that preliminary data from studies in the U.S., Canada and Europe has indicated that MRI is able to locate approximately 2 percent more breast cancer than traditional mammography. Importantly, Harms also emphasized that MRI was able to reliably rule out cancer (with a near 100% "negative predictive value") in high-risk women who may otherwise have been considering prophylactic mastectomy or other aggressive treatment options.
Harms said that the use of MRI would especially benefit young premenopausal women with dense breast tissue, women with a strong family history of the disease, and women who have silicone implants.
A second presentation at the conference focused on the use of MRI to accurately measure a patient's response to treatment. Dr. Laura Esserman of the University of California, San Francisco and colleagues studied 33 patients with Stage II or III breast cancer who underwent four cycles of chemotherapy and MRI scanning. They found that MRI could accurately measure changes in tumor size as a direct result of the chemotherapy, giving doctors an important tool for assessing the effectiveness of the treatment being given.
"MRI can be a catalyst for change because it gives us a chance to visualize tumors and clearly observe a response," Esserman told the attendees. Beyond the size of a tumor, she added, MRI can also assess a tumor's pattern, heterogeneity, vascularity and volume.
Esserman cautioned, however, that MRI was not able to distinguish between residual ductal carcinoma in situ and residual cancer.
Both of the above studies confirm a growing body of research that is touting the advantages of using MRI for both screening and detection of breast cancer, especially in younger women with dense breasts or those at especially high risk for the disease. However, the widespread use of MRI for breast cancer is still years away, primarily because of the cost of the MRI machine and testing.
In the interim, another screening tool, ultrasound, is becoming an increasingly important new diagnostic option for breast cancer.
Breast ultrasound sends high-frequency sound waves through the breast, which are then picked up and translated by a computer into an image that is displayed on a screen. 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.
However, ultrasound's use as a regular screening tool for most women is not recommended because small calcium deposits, which are one of the earliest signs of breast cancer, are not visible by ultrasound.
Approximately two-thirds of premenopausal women have dense breasts. In postmenopausal women, about one-quarter have dense breasts, and the rate increases to about half of postmenopausal women who take hormones. Breast density is the most significant factor in predicting the sensitivity-and thus accuracy-of a mammogram. As the density of breast tissue increases, the sensitivity of a mammogram decreases.
A major study last year by a group of radiologists in New York City found that a combination of mammography and ultrasound can provide dramatic improvements in detecting breast cancers in women with dense breast tissue. Dr. Thomas Kolb and colleagues conducted more than 18,000 breast cancer screenings using mammography, ultrasound and physical clinical exams, either alone or in combination.
Breast density is traditionally rated on a scale of one to four, with Grade Four being the most dense. The researchers found that a combination of mammography and ultrasound detected 100 percent of the breast cancers in women with Grade Two density breasts, 94 percent in women with Grade Three, and 88 percent in women with Grade Four density breasts.
Mammography alone detected 83 percent of cancers in women with Grade Two breast densities, decreasing to just over half (55 percent) in women with the densest breast tissue. Conversely, ultrasound, when used alone, detected two-thirds (66 percent) of the cancers in Grade Two, but improved to a 75 percent detection rate in Grade Four density breasts.
Physical examination of breast tissue (without mammography or ultrasound) was found to be the least sensitive method of detecting breast cancers, and by the time tumors could be felt they were usually in a more advanced stage.
Kolb explained that ultrasound is more effective than mammography in detecting cancer in women with dense breasts because of its ability to "contrast" breast tissue. In ultrasound, dense breast tissue appears white, while the cancer is dark. Conversely, in a mammographic image, both the dense breast tissue and the cancer are white, making it more difficult to distinguish between the two.
More than 700,000 women undergo breast biopsies each year. But nearly 80 percent of these biopsies are benign (non-cancerous). In effect, if a more accurate non-invasive diagnostic technique were available, hundreds of thousands of women would be spared from unnecessary biopsy procedures.
While ultrasound is certainly not the answer to this dilemma, it is clearly a step in the right direction. One study estimated that the use of ultrasound could eliminate as many as 20 percent of these invasive biopsies. Furthermore, unlike a mammogram that uses a small (and safe) amount of radiation, ultrasound is a noninvasive test that uses sound waves. It also doesn't require the breast compression that many women find painful in mammograms.
Yet, while ultrasound, MRI and other emerging technologies are proving valuable in detecting breast cancers at earlier, more treatable stages, regular mammography screening still remains the most effective early screening option for women. The American Cancer Society and most cancer organizations strongly recommend that every woman have a mammogram each year beginning at age 40.
SOURCES:
17th Annual Miami Breast Cancer Conference, Miami Beach, Florida, March 7, 2001
American Institute of Ultrasound in Medicine (http://www.aium.org)
The Susan G. Komen Breast Cancer Foundation (http://www.komen.org)
The American Cancer Society (http://www.cancer.org)
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