Like a colorblind coach who can see all the players but cannot tell who is friendly, x-ray mammography is effective in finding suspicious breast lesions but is not reliable in determining which ones are cancerous. Because of this uncertainty, about 500,000 women have their breast lesions examined by surgical biopsy each year, even though most biopsies show the tissue to be benign.
Research carried out at the University of Wisconsin Medical School in Madison suggests that MRI can clear up many questions left unanswered by conventional imaging systems, and may significantly reduce the number of surgical breast biopsies.
A recent study led by diagnostic radiologist Dr. Frederick Kelcz used special MRI techniques to classify 72 breast lesions in 70 women at the University of Wisconsin Hospital and Clinics. By comparing MRI-based predictions with biopsy results, Kelcz' team was able to correctly predict 50 of 55 benign lesions and 14 of 17 malignant lesions. Kelcz presented findings from the 3-year study at a recent Radiological Society of North America meeting.
"In our study, MRI could have reduced the unnecessary biopsy rate by 90%," Dr. Kelcz said. "Even though MRI is expensive, surgical biopsy is several times more costly. Ultimately, MRI may prove cost-effective for determining which women really need biopsy."
Women in the study were examined with dynamic, enhanced MRI when a mammogram or breast examination suggested a problem requiring biopsy. The women were injected with a dye during a rapid series of MRI images. In general, the faster the magnetic dye was absorbed by a breast mass, the more likely it was that the mass was malignant. In the current study, about one-third of breast abnormalities did not take up the dye, and all of these were benign, Dr. Kelcz said.
The University of Wisconsin study is part of a worldwide effort to improve the technology used in diagnosing and managing cancer and other breast problems. Mammography is the most cost-effective method for the large-scale detection of breast abnormalities. But signs of malignancy can be subtle on x-ray film, where all breast tissues overlap. This makes it difficult for doctors to find or classify some abnormalities, said Dr. Kelcz, who is Associate Professor of Radiology at the University of Wisconsin Medical School.
Magnetic resonance imaging, which produces cross-sectional pictures of soft tissue, has rapidly become the primary imaging method for diagnosing brain and spinal cord abnormalities and checking breast implants for leakage. "MRI won't replace mammography or biopsy, but it may become an important problem-solving tool for breast cancer," Dr. Kelcz said. The study suggested several situations in which MRI might supplement a mammographic examination:
When a suspected cancerous lesion can be seen only on one mammographic view, as can happen with the dense glandular breast tissue common in younger women and in older women on hormonal therapy
When deciding between lumpectomy or mastectomy (MRI may reveal previously undetected lesions, suggesting an advantage to mastectomy.)
After lumpectomy to ensure that all malignant tissue has been removed and to distinguish scar tissue from recurrent tumor
When a mammogram shows multiple lesions in a woman with a strong family history of breast cancer.
Dr. Kelcz cautioned that MRI should not be used as a general substitute for mammography or biopsy. "MRI alone would have misdiagnosed three cancers detected by mammography, so we advise patients with a negative MRI to get at least two follow-up examinations at six month intervals to make sure that the abnormality is not growing,"' he said. The Madison researchers are working to increase MRI's predictive accuracy.
In addition, the study showed that it isn't cost-effective to use MRI when conventional imaging systems suggest a lesion with a high likelihood of being either benign or malignant, Dr. Kelcz said. Magnetic resonance imaging also can be inaccurate in trying to diagnose malignancy when mammography shows a small cluster of very tiny calcifications.
Dr. Kelcz' interest in breast MRI stemmed from his experience in interpreting mammograms: "For other parts of the body, we have several methods to help us decide whether or not an abnormality is cancer," he said. "In the breast, however, there was little we could suggest aside from biopsy or follow-up mammography."
In the future, MRI could provide essential information to women who have a strong family history of breast cancer or who test positive for the "breast cancer gene" but have negative mammograms, Dr. Kelcz speculated.