Superparamagnetic iron oxide-enhanced MRI at 3 T for accurate axillary staging in breast cancer.

Background: The aim of this study was to evaluate whether MRI at 3T with superparamagnetic iron oxide (SPIO) enhancement is an accurate and useful method for detecting metastases in sentinel nodes identified by CT-lymphography (CT-LG) in patients with breast cancer. The results were compared with those obtained using CT-LG alone and diagnosing metastasis according to size criteria. Methods: Patients with clinically node-negative breast cancer were included. Sentinel nodes identified by CT-LG were evaluated prospectively using SPIO-enhanced MRI at 3T. Sentinel node size was measured on CT-LG, and a node larger than 5 mm in short-axis diameter was considered metastatic. Sentinel nodes localized by CT-LG were removed, and imaging results and histopathological findings were compared. Results: Sentinel nodes were identified successfully by CT-LG in 69 (99 per cent) of 70 patients. All 19 patients with a finding of metastasis in sentinel nodes at pathology were also shown to have metastases on MRI. Forty-eight of 50 patients with non-metastatic sentinel nodes diagnosed at pathology were classified as having non-metastatic nodes on MRI. On a patient-by-patient basis, the sensitivity, specificity and accuracy of MRI for the diagnosis of sentinel node metastases were 100, 96 and 97 per cent; respective values for CT-LG were 79, 56 and 62 per cent. The specificity and accuracy of MRI were superior to those of CT-LG (P < 0.001 and P = 0.002 respectively). Conclusion: SPIO-enhanced MRI at 3T is useful for accurate diagnosis of metastatic sentinel nodes, indicating that sentinel node biopsy may be avoided in patients with breast cancer who have non-metastatic sentinel nodes on imaging.