Conventional Imaging, MRI and (18)F-FDG PET/MRI for N and M Staging in Patients with Newly Diagnosed Breast Cancer

SIMPLE SUMMARY: (18)F-FDG PET/MRI is superior in nodal staging in patients with newly diagnosed breast cancer compared to conventional imaging by sonography, CT and bone scintigraphy and compared to MRI alone. (18)F-FDG PET/MRI correctly detects not only nodal positive status in significantly more patients, but also classifies this positive nodal status into the correct clinical lymph node stage more often than conventional imaging and than MRI alone. (18)F-FDG PET/MRI may be a future tool as a potential alternative to invasive staging procedures for assessing the N stage. In terms of the detection of distant metastases, there is a trend towards a higher sensitivity of MRI and (18)F-FDG PET/MRI, which, however, did not show significant differences compared with conventional staging by CT and bone scintigraphy. This demonstrates that the imaging currently recommended by multiple guidelines seems to be sufficient for the staging of distant metastases. ABSTRACT: Background: This study compares the diagnostic potential of conventional staging (computed tomography (CT), axillary sonography and bone scintigraphy), whole-body magnetic resonance imaging (MRI) and whole-body (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET/)MRI for N and M staging in newly diagnosed breast cancer. Methods: A total of 208 patients with newly diagnosed breast cancer were prospectively included in this study and underwent contrast-enhanced thoracoabdominal CT, bone scintigraphy and axillary sonography as well as contrast-enhanced whole-body (18)F-FDG PET/MRI. The datasets were analyzed with respect to lesion localization and characterization. Histopathology and follow-up imaging served as the reference standard. A McNemar test was used to compare the diagnostic performance of conventional staging, MRI and (18)F-FDG PET/MRI and a Wilcoxon test was used to compare differences in true positive findings for nodal staging. Results: Conventional staging determined the N stage with a sensitivity of 80.9%, a specificity of 99.2%, a PPV (positive predictive value) of 98.6% and a NPV (negative predictive value) of 87.4%. The corresponding results for MRI were 79.6%, 100%, 100% and 87.0%, and were 86.5%, 94.1%, 91.7% and 90.3% for (18)F-FDG PET/MRI. (18)F-FDG PET/MRI was significantly more sensitive in determining malignant lymph nodes than conventional imaging and MRI (p < 0.0001 and p = 0.0005). Furthermore, (18)F-FDG PET/MRI accurately estimated the clinical lymph node stage in significantly more cases than conventional imaging and MRI (each p < 0.05). Sensitivity, specificity, PPV and NPV for the M stage in conventional staging were 83.3%, 98.5%, 76.9% and 98.9%, respectively. The corresponding results for both MRI and (18)F-FDG PET/MRI were 100.0%, 98.5%, 80.0% and 100.0%. No significant differences between the imaging modalities were seen for the staging of distant metastases. Conclusions: (18)F-FDG PET/MRI detects lymph node metastases in significantly more patients and estimates clinical lymph node stage more accurately than conventional imaging and MRI. No significant differences were found between imaging modalities with respect to the detection of distant metastases.