Identification of Axillary Lymph Node Metastasis in Patients With Breast Cancer Using Dual-Phase FDG PET/CT.

OBJECTIVE. The aim of this study was to assess the diagnostic performance of dual-phase 18F-FDG PET/CT in detecting axillary lymph node metastasis in patients with breast cancer. MATERIALS AND METHODS. A total of 826 patients with breast cancer were retrospectively evaluated. PET/CT scans were performed 1 hour and 2 hours after FDG administration before treatment. The maximum standardized uptake value (SUVmax) in the axillary lymph node at both time points (hereafter referred to as SUVmax1 and SUVmax2, respectively) and the retention index (RI) were calculated. RESULTS. Axillary lymph node metastasis was detected in 285 of 826 patients (34.5%). The median axillary SUVmax1, SUVmax2, and RI in patients with nodal metastasis were higher than those in patients without metastasis (1.5 vs 0.6, 1.6 vs 0.5, and 7.7 vs -3.7, respectively; all p < 0.001). The diagnostic accuracy of axillary SUVmax1 and SUVmax2 was equivalent, and the sensitivity and specificity of SUVmax1 were 74.7% and 83.4%, respectively. Although the performance of the axillary RI was inferior to that of SUVmax1 and SUVmax2, both the SUVmax and the RI were independent predictors of nodal metastasis, and a positive RI suggested axillary lymph node involvement when the SUVmax1 was significantly high. Of 533 patients with category T1-2 breast cancer without lymph node swelling, 101 (19.0%) had pathologic lymph node involvement; the negative predictive value of axillary SUVmax1 was 86.8%. CONCLUSION. Delayed phase imaging identified axillary lymph node metastasis as accurately as standard PET/CT. A high negative predictive value of PET/CT for the detection of nodal metastasis is helpful to avoid surgical axillary assessment in patients with category T1-2 breast cancer without lymph node swelling.