Diagnostic Potential of Apparent Diffusion Coefficient-Based Lymph Node Classification in Breast Cancer Patients...

Background/Objectives: To evaluate the diagnostic potential of apparent diffusion coefficient (ADC) values for classifying lymph nodes as benign or malignant in breast cancer patients undergoing [¹⁸F]FDG-PET/MRI staging. Methods: Mean ADC values and short-axis diameters (±standard deviation) of 199 thoracic lymph nodes in 113 newly diagnosed breast cancer patients were retrospectively analyzed. All patients underwent [¹⁸F]FDG-PET/MRI staging, between July 2017 and June 2021. A node-by-node comparison was performed with respect to pathological node status. Nodal FDG uptake in whole-body [¹⁸F]FDG-PET/MRI served as reference standard for nodal malignancy. Group comparison using Mann-Whitney U test, receiver operating characteristic curve (ROC) analysis and diagnostic performance were calculated. p values below 0.05 were defined as statistically significant. Confidence intervals (CI; 95%) were calculated. Results: Ninety-three lymph nodes were FDG-negative while 106 lymph nodes were FDG-positive. FDG-negative lymph nodes had significantly lower short-axis diameters ((5.1 ± 1.5 mm versus 12.3 ± 5.3 mm); p < 0.01; U: 405.50; Z: -11.24). ADC values were significantly lower in FDG-positive lymph nodes (0.72 ± 0.14 × 10^-3 mm²/s) than in FDG-negative lymph nodes ((1.18 ± 0.18 × 10^-3 mm²/s); p < 0.01; U: 173.00; Z: -11.80). ROC analysis and Youden's index revealed an ADC cut-off of 0.95 × 10^-3 mm²/s (AUC: 0.98; p < 0.01; 95% CI: 0.96-1.01). According to the calculated cut-off, sensitivity, specificity, and accuracy of ADC values for differentiating FDG-negative from FDG-positive lymph nodes were 98%, 97% and 97%, respectively. Conclusions: ADC values derived from MRI were significantly associated with FDG uptake in this retrospective cohort and may serve as a complementary imaging biomarker for lymph node characterization.