Breast MRI: The Radiologist's Perspective
Breast MRI: The Radiologist's Perspective
Drs. Bleicher and Morrow have written a review on the use of breast magnetic resonance imaging (MRI) from the surgeon's perspective, with an emphasis on clinical outcomes. They give an overview of the clinical uses where breast MRI has been shown to contribute to the diagnosis and work-up of breast cancer, such as high-risk screening and axillary adenopathy of an unknown primary. On the other hand, they raise concern about the use of breast MRI in patients with a recent diagnosis of breast cancer. This commentary will focus on screening the high-risk woman and evaluating the breasts of women with a new breast cancer diagnosis.
When reviewing the literature on breast MRI, it should be recognized that the field is not static, and the breast MRI of just 5 years ago is not the same as that of today. There have been significant advances in technique over the past 5 years, with the advent of newer sequences (such as parallel imaging) that allow fast simultaneous acquisition of both breasts using high resolution. These improvements in technique translate into improved image quality, allowing easier clinical use and more precise interpretation. Perhaps the most important development has been the ability to percutaneously vacuum biopsy suspicious findings, so that a surgical procedure is not required for diagnosis. These advances have allowed breast MRI to be used much more easily in the clinical setting.
Accreditation Standards and Guidelines
Along with the advances in technique, the American College of Radiology (ACR) has taken a leadership role and convened a committee to establish an accreditation process to standardize technique and ensure the quality of breast MRI. In order for a facility to be accredited, image quality needs to pass rigorous standards, ability to biopsy suspicious lesions must be demonstrated, and ongoing training and interpretation of a minimal number of cases are mandatory for interpreting radiologists. As with other areas of breast imaging such as mammography, oversight is required. In this regard, patients will be assured of receiving a high-quality examination, and interpreting radiologists will be able to provide referring physicians with completed work-ups. Along with these improvements in the field, numerous instructional courses sponsored by the College have been started over the past few years to train radiologists in interpretation and MR intervention.
Despite all these improvements, there are still debates over which clinical situations warrant evaluation with breast MRI. Current clinical guidelines for breast MRI from the ACR address high-risk screening, extent of disease evaluation in the preoperative setting of both breasts in a new breast cancer diagnosis, postoperative evaluation for positive margins following lumpectomy, and response of breast cancer to neoadjuvant chemotherapy. Other indications include axillary node metastasis of an unknown primary, Paget's disease, evaluation of suspected recurrent cancer and an abnormal mammogram or physical examination that cannot be resolved by conventional imaging.
Numerous trials have shown that annual breast MRI can detect occult cancer in high-risk women. The American Cancer Society has therefore recommended annual screening with MRI in women with a BRCA1 or BRCA2 mutation, an untested first-degree relative of a known carrier, prior mantle radiation for Hodgkin's disease, and a greater than 20% cumulative life-time risk of breast cancer. Patients with rare syndromes such as Li-Fraumeni and Cowden are also recommended to undergo annual MRI screening.
The recommendation to screen with MRI was made without evidence from randomized controlled trials demonstrating mortality benefit. Even though mortality benefit is the ultimate standard for a screening test, it is highly unlikely that such a trial could be mounted today. We live in a world of rapidly expanding technology and innovation, where newer diagnostic technologies are often quickly evaluated and adopted. Surrogate markers such as small tumor size and negative nodal status (markers that are responsible for reducing the mortality seen with screening mammography) have been used to justify recommendations. No data suggest that cancer detected by MRI is any different than cancer detected by mammography, and therefore, the detection of small node-negative cancer is adequately compelling evidence to recommend screening.
The authors are correct in emphasizing that screening with MRI is an added level of surveillance above and beyond mammography, resulting in its own possibility of call-backs and biopsy for suspicious findings. Therefore, the decision to screen with MRI is not one to be taken lightly. Call-back rates and biopsy rates with breast MRI appear reasonable in high-risk groups where the cancer yield is high.
Areas of Controversy