Determining the Axillary Nodal Status with 4 Current Imaging Modalities, Including 18F-FDG PET/MRI, in Newly Diagnosed Breast Cancer: A Comparative Study Using Histopathology as the Reference Standard

The purpose of this study was to compare breast MRI, thoracic MRI, thoracic 18F-FDG PET/MRI, and axillary sonography for the detection of axillary lymph node metastases in women with newly diagnosed breast cancer. Methods: This prospective double-center study included patients with newly diagnosed breast cancer between March 2018 and December 2019. Patients underwent thoracic (18F-FDG PET/)MRI, axillary sonography, and dedicated prone breast MRI. Datasets were evaluated separately regarding nodal status (nodal-positive vs. nodal-negative). Histopathology served as the reference standard in all patients. The diagnostic performance of breast MRI, thoracic MRI, thoracic PET/MRI, and axillary sonography in detecting nodal-positive patients was tested by creating receiver-operating-characteristic curves (ROC) with a calculated area under the curve (AUC). Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated for all 4 modalities. A McNemar test was used to assess differences. Results: In total, 112 female patients (mean age, 53.04 ± 12.6 y) were evaluated. Thoracic PET/MRI showed the highest AUC, with a value of 0.892. The AUCs for breast MRI, thoracic MRI, and sonography were 0.782, 0.814, and 0.834, respectively. Differences between thoracic PET/MRI and axillary sonography, thoracic MRI, and breast MRI were statistically significant (PET/MRI vs. axillary sonography, P = 0.01; PET/MRI vs. thoracic MRI, P = 0.02; PET/MRI vs. breast MRI, P = 0.03). PET/MRI showed the highest sensitivity (81.8% [36/44]; 95% CI, 67.29%–91.81%), whereas axillary sonography had the highest specificity (98.5% [65/66]; 95% CI, 91.84%–99.96%). Conclusion: 18F-FDG PET/MRI outperforms axillary sonography, breast MRI, and thoracic MRI in determining the axillary lymph node status. In a clinical setting, the combination of 18F-FDG PET/MRI and axillary sonography might be considered to provide even greater accuracy in diagnosis.