October 6, 2008
Breast MRI: A Case for Wider Use
By Kamilia F. Kozlowski, MD
Vol. 9 No. 20 P. 20
In March 2007, the American Cancer Society (ACS) updated its breast cancer screening recommendations to include annual breast MRI for women who are at high risk of developing breast cancer in their lifetime. The ACS based its recommendation on 10 years of evidence from international studies that breast MRI can detect cancers not seen on mammography or ultrasound.
While screening mammography has proven to reduce the mortality rate from breast cancer, mammography still misses 20% to 25% of breast malignancies.1,2 Mammography has shown to be less effective in women with dense breasts, which is one half of the female population. In these women, malignancies can have the same density as normal tissue, making them difficult to detect on conventional mammography. Mammography also is not as effective in women with implants or those who have had previous breast surgery or radiation.
Breast MRI and Ductal Cancer
Originally, breast MRI was not considered as effective as mammography for detecting ductal carcinoma in situ (DCIS), a very early stage of breast cancer found in the lining of the breast ducts. Up to 30% of all new breast carcinomas are DCIS.3 It is important to detect DCIS before it spreads because, if treated aggressively, it can be 100% curable.
However, growing evidence suggests that breast MRI may be even better at detecting DCIS than mammography. In the August 2007 issue of Lancet, researchers from Germany reported that MRI detected almost twice as many cases of DCIS as mammography. They studied MRI and mammography results of more than 7,000 women.4 They found that MRI detected 92% of the DCIS cases (153 of 167), which was significantly more than the 56% (93 of 167) detected by mammography, including additional views. In addition, they found that MRI detected 98% of the 89 cases of high-grade DCIS, which is believed to be the most likely form to become invasive cancer, whereas mammography missed 48% of these cases.
MRI also has proven beneficial in women newly diagnosed with breast cancer. Up to 10% of women are likely to have cancer in the opposite breast at the time of their original diagnosis. Researchers led by Constance D. Lehman, MD, PhD, director of breast imaging at the Seattle Cancer Care Alliancce and an association professor in the radiology department at the University of Washington in Seattle, found that MRI could detect more cases of contralateral breast cancer in women newly diagnosed than either clinical breast exams or mammography.5 They studied 969 women who had recently been found to have cancer in one breast but whose opposite breast appeared to be normal. With MRI, they found 30 women (3.1%) had a cancer in the opposite breast that had not been detected earlier. Studies also show that MRI can detect additional cancer sites in the same breast 16% of the time.6
Dedicated breast MRI also has been found to be extremely useful in treatment planning. Studies have shown that breast MRI more accurately assesses tumor size and spread than mammography or ultrasound, enabling oncology surgeons and their patients to determine whether the best course of treatment is lumpectomy or mastectomy. With mammography and ultrasound, it can be difficult, if not impossible, to see the chest wall and whether the cancer has spread to that area.
Since the ACS updated its screening recommendation, more high-risk women have come to our comprehensive breast center in Tennessee to have breast MRI. We have had a dedicated breast MRI system at our center since the fall of 2002, which delivers 1-millimeter slices that enable us to find early cancers in women whose mammograms and even MRIs, done elsewhere on whole body machines with breast coils, were negative for disease. We are able to image both breasts at the same time, greatly reducing the risk of missing cancer in the contralateral breast.
The ACS relies on predictive models to define high risk as those who have a 20% to 25% lifetime risk of developing breast cancer, which is still the leading cause of cancer death among American women aged 40 to 55. Women who fall into the high-risk category include those with BRCA1 and BRCA2 cancer gene mutations; first-degree relatives of those with a BRCA1 or BRCA2 mutation, even if they have yet to be tested themselves; women who have had radiation to the chest between the ages of 10 and 30; and women who have Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome or may have one of these syndromes based on the history of a first-degree relative.
Approximately 1.4 million women are estimated to fall into one or more of these high-risk groups. Keep in mind, though, that 80% of breast cancer is found in women who do not have a history of the disease.7
Because the cost of breast MRI is 10 times that of a mammogram, some insurers balk at reimbursement for the exam. Some also argue that while breast MRI has a high sensitivity rate—nearly 100% for lesions larger than 3 millimeters—it also has low specificity, which can result in many false-positive findings.8 While economic and emotional concerns about false positives are valid, like most breast specialists, I would not want to miss the opportunity to find a very small breast cancer, especially today when we can treat most early-stage cancers so successfully. Also, the high false-positive rates we are currently seeing with breast MRI seem to be declining as breast specialists gain more experience interpreting the images and as the clarity of 3D images improves.
Initially, there was some reluctance on the part of physicians to have their patients undergo breast MRI because of the increased costs of their workup and finding additional lesions (about 20%) only on MRI. If doctors could not correlate the MRI findings on second-look ultrasound and did not have MRI biopsy capability, the thinking was that it may be better not to have a breast MRI. But as breast MRI biopsy capabilities on dedicated breast MRI systems have improved, I believe that dilemma has been eliminated. With today’s breast MRI capabilities and its ability to detect occult cancers on both mammography and breast ultrasound, I think breast MRI should become part of routine practice for more than just women who are at high risk.
I am not alone in calling for breast MRI’s expanded role in fighting a disease that still claims about 40,000 lives each year. In the June issue of Radiology, Ferris Hall, MD, wrote that breast MRI should be recommended for many women at only 14% (one in seven) lifetime risk of breast cancer. One in seven is the risk of the average American woman. Also, at the European Conference on Radiology held in Vienna, Austria, in March, prominent physicians Christiane Kuhl, MD, a professor of radiology and vice chairman of the radiology department at the University of Bonn, and Christopher Riedl, MD, of the radiology department at the Memorial Sloan-Kettering Cancer Center, said more women should have breast MRI because it is the most sensitive screening tool available.
The need to perform percutaneous biopsy under MRI guidance emerged in part because of the modality’s sensitivity. The kinetics and morphology of lesions are important. To date, there is no consensus about what constitutes clinically important contrast enhancement on breast MRI. However, it is generally agreed that cancers tend to demonstrate a washout kinetic curve; the contrast (typically IV-administered gadolinium) goes in fast and washes out rapidly. Benign changes will show a progressive curve, where the lesion continues to take up contrast with time. There also is an intermediate curve, where the contrast rises and then plateaus.
Lesions that demonstrate an intermediate curve could be either benign or malignant and are the most difficult to differentiate. They often are the ones that need biopsy. Whether the suspicious region needs to be biopsied also depends on the morphology of the mass, which may have the most prognostic value. Spiculated and irregular margins are more indicative of a carcinoma than smooth margins.
Like stereotactic and ultrasound-guided biopsy, MRI-guided percutaneous biopsy is less invasive than surgery, costs less—no operating room needed or general anesthesia administered—and is less likely to cause side effects or complications such as bleeding or infection. Done under local anesthesia, MRI-guided biopsy also eliminates the risks of general anesthesia. Our facility uses Aurora Imaging Technology’s 1.5T breast MRI system and its AuroraBIOPSY system. We’ve found them easy to use and reasonably comfortable for the patient, who is asked to stay still during the procedure.
Because suspicious lesions wash out quickly, the coordinates must be determined during the initial targeting. The biopsy automatically calculates the needle placement, helping to reduce human errors from manual calculations. With the Aurora system, the physician clicks on the lesion clearly displayed on the computer monitor and then clicks on the marker; the integrated stereotactic guidance system then directs the needle to precisely where it needs to be. Physician involvement in the biopsy procedure takes about 15 to 20 minutes. Integrated paddles help the patient stay perfectly still, so the lesion is targeted more precisely. The system also allows for medial and lateral approaches. It provides access to lesions that are close to the chest wall and the sternum.
The Aurora System allows for multiple targets to be biopsied sequentially; however, there are limits to the amount of contrast that can be administered in a 24-hour period. If the patient has multiple lesions, biopsies may need to be scheduled on different days. Once the procedure is complete, a marker or clip is placed in the target area and a follow-up mammogram is performed to check its placement. If the pathology report is negative, we order a follow-up MRI. If there is no enhancement on the follow-up MRI, we can be assured that the targeted lesion was indeed benign.
Breast MRI has been evolving over the past 20 years. Studies show it to be the most sensitive imaging modality for breast cancer available. Women who are at high risk for developing breast cancer in their lifetime are encouraged to have annual breast MRI screenings along with their mammograms, preferably alternately with mammography every six months if they are BRCA positive, to detect cancers in their earliest stages when they are most treatable. MRI has demonstrated high sensitivity for high-grade DCIS, which is the most likely form of this early-stage cancer to develop into invasive disease. Breast MRI has shown to be even more sensitive for DCIS than mammography.4
Percutaneous biopsy capabilities on MRI equipment have made the modality a more valuable tool for fighting breast cancer. Some lesions only can be seen on MRI and, if they are, they may need further investigation with biopsy or excision. While the cost of breast MRI is about 10 times that of mammography, what it can save the healthcare system in the long run is arguably more important. Until the cost is lowered significantly, breast MRI won’t replace mammography as a screening modality, but I believe it should be made available to women who have been diagnosed with breast cancer and to women whose lifetime risk is double the average risk, not triple as currently recommended in the ACS breast MRI screening guidelines.
— Kamilia F. Kozlowski, MD, is the medical director and clinical breast radiologist at the Knoxville Comprehensive Breast Center in Tennessee. She is president of the Aurora Breast MRI Society, a group for users of the Aurora systems.
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