Magnetic resonance imaging for diagnosis, staging, and follow-up

Abstract

There is considerable debate regarding the role of magnetic resonance imaging (MRI) in the management of the breast cancer patient. MRI should not be used as a diagnostic test to exclude the presence of carcinoma. In one multi-institutional study of 1,004 women, the positive predictive value of MRI was 72%, and the overall sensitivity 88% [1]. Recognition that MRI identifies additional areas of cancer not detected by other imaging modalities in an average of 16% of breast cancer cases [2] has led to great interest in its use to select women for breast-conserving surgery (BCS). Suggested benefits of MRI include a reduction in margin positivity and conversion from BCS to mastectomy, and a decrease in local recurrence rates. Several retrospective studies and one prospective randomized [3] trial have addressed the impact of MRI on the short-term surgical outcomes. These studies have uniformly failed to demonstrate a benefit for MRI. In the prospective randomized Comparative Effectiveness of Magnetic Resonance Imaging in Breast Cancer (COMICE) trial, re-excision was required in 10% of the MRI group and 11% of the non-MRI group, with conversion to mastectomy in 6% and 8%, respectively. Most studies show that MRI approximately doubles the overall likelihood of undergoing mastectomy without decreasing unplanned mastectomy. Solin and colleagues examined the effect of MRI on local recurrence after BCS with radiation therapy (RT) and on contralateral cancer [4]. At 8 years the incidence of contralateral cancer was 6% in both the MRI and non-MRI groups, and local recurrence was seen in 3% of those with an MRI at diagnosis and in 4% of those without. The repeated observation that MRI finds two to four times as much disease as becomes evident as local recurrence indicates that the majority of this disease is controlled with RT. In addition, the existence of local recurrence after mastectomy indicates that some local recurrence is a manifestation of biologically aggressive disease (first site of metastases), which is unlikely to be influenced by the use of MRI. Current indications for the use of MRI in patients with breast cancer include: known or suspected BRCA1&2 mutation carriers who choose not to undergo bilateral mastectomy; patients presenting with metastases to the axillary nodes and no evident breast tumor; patients with Paget's disease of the nipple and no evident breast tumor; or the uncommon patient with a major discrepancy between clinical findings and the results of mammography and ultrasound. A benefit for MRI in the follow-up of the breast cancer patient is also unproven. Local recurrence after BCS and RT is uncommon, occurring in fewer than 8% of patients at 10 years. The size of the local recurrence is not a prognostic factor, and the idea that early detection will improve prognosis does not reflect the biology of local recurrence. The treatment of local recurrence regardless of size is mastectomy, and salvage mastectomy results in local control in 85 to 95% of patients. These good outcomes must be weighed against the cost of MRI, the high rate of short-interval follow-up and biopsies generated, and the lack of a clear rationale for using the examination for follow-up.