HOLLYWOOD, FLA. — A cautious footnote about the use of magnetic resonance imaging to stage breast cancer or to gauge response to breast cancer therapy was added to guidelines from an alliance of 21 leading cancer centers.
“The value of MRI is uncertain, practice varies, and the potential downsides are real,” Dr. Stephen B. Edge said at the annual conference of the National Comprehensive Cancer Network.
“This is a rapidly evolving area in practice. This is an area where there is no consensus,” he said.
To guide clinicians on the utility of MRI in breast cancer, NCCN added six new recommendations to the Principles of Dedicated Breast MRI Testing section of the guidelines. (Unless noted, all are grade 2A recommendations, reflecting uniform consensus from NCCN panel members.)
This section said that MRI may be useful to stage the extent of cancer or to detect multifocal or multicentric disease in the ipsilateral breast, or to screen the contralateral breast at time of diagnosis (a category 2B recommendation, which has the same level of evidence as a 2A recommendation, but with nonuniform NCCN consensus).
“The impact of identification of contralateral cancers is unclear,” Dr. Edge said. MRI leads to frequent biopsies, 75%–80% of which are benign, he added. For example, in an MRI screening study of 969 women with a normal mammogram, 121 had a biopsy-based on MRI lesion detection, and 30 (3%) of the 969 women had a diagnosis of contralateral cancer (N. Engl. J. Med. 2007;356:1295–303).
MRI may also be useful before and after neoadjuvant therapy to define the extent of disease or response to therapy. In addition, “MRI can help assess candidacy for surgery after adjuvant therapy,” said Dr. Edge, chair of the department of breast surgery and medical director of the Breast Center at Roswell Park Cancer Institute in Buffalo, N.Y.
However, MRI findings may underestimate residual disease, he said. In one study, “unfortunately, half of women cleared by MRI still had residual tumor at time of surgery” (Br. J. Cancer 2004;90:1349–60). “So, complete clearance on MRI does not mean complete clinical clearance. There is clearly a need for prospective data in this field.”
In addition, MRI may be useful to identify primary cancer in women with axillary node adenocarcinoma or with Paget's disease of the nipple when primary breast disease is not identified on mammography, ultrasound, or physical exam.
Also, because of a high rate of false-positive findings, the panel concluded that surgical decisions should not be based solely on MRI findings.
For example, a multicenter study of 426 women with a suspicious mammogram and proven cancer revealed a 24% incidental lesion false-positive rate with MRI, compared with 10% false-positive rate with mammography (J. Surg. Oncol. 2005;92:32–8). “But MRI also detected some additional lesions,” Dr. Edge said.
An unanswered question is whether MRI affects long-term breast cancer outcome and survival, Dr. Edge said. “The only available evidence—retrospective data—shows no impact of MRI on local recurrence or survival.”
Another updated NCCN guideline, this one on breast cancer screening and diagnosis, states that physicians can consider MRI as an adjunct to screening high-risk women in addition to annual mammography and breast exam. New definitions of high-risk patients include women aged 25 years and older with a history of thoracic radiotherapy, and those with a lifetime risk of breast cancer exceeding 20%. MRI is not recommended for screening average-risk women.
The NCCN guidelines panel also included MRI expertise recommendations. For example, an expert breast-imaging team should perform and interpret breast MRI examinations, working in concert with a multidisciplinary treatment team.
In addition, breast MRI should be done by a radiologist with expertise in breast imaging using a dedicated coil. Also, an imaging center should have the ability to perform MRI-guided needle sampling and/or wire localization of relevant findings.