Value of 68Ga-PSMA HBED-CC PET for the assessment of lymph node metastases in prostate cancer patients with biochemical recurrence: Comparison with histopathology after salvage lymphadenectomy

The purpose of this study was to evaluate the accuracy of Glu-NH-CONH- Lys-(Ahx)-[68Ga(HBED-CC)] PET compared with morphologic imaging for the assessment of lymph node metastases (LNM) in patients with recurrent prostate cancer. Methods: Forty-eight patients (median age, 71 y; interquartile range, 66-74 y) with biochemical recurrence (median prostate-specific antigen level, 1.31 ng/mL; interquartile range, 0.75-2.55 ng/mL) who underwent ⁶⁸Ga-prostate-specific membrane antigen (PSMA) HBED-CC PET/CT or PET/MR and salvage lymphadenectomy were retrospectively included. Institutional review board approval and written informed consent were obtained from all patients for the purpose of anonymized evaluation and publication of their data. Standardized predefined lymph node (LN) template fields (n 5 10) were evaluated in 68Ga-PSMA HBED-CC PET and morphologic imaging for the presence of LNM using a 5-point-scale. Additionally, SUVmean/max and size of suspicious lesions were determined. Specificity of ⁶⁸Ga- PSMA HBED-CC PET imaging for PET-positive LNs was defined by comparison to histopathology. The diagnostic accuracy of ⁶⁸Ga-PSMA HBED-CC PET compared with morphologic imaging alone was assessed, and areas under the receiver-operating-characteristic curves are presented. Results: LNM were found histologically in 68 of 179 resected anatomic LN fields (38.0%). The specificity of ⁶⁸Ga-PSMA HBED-CC PET and morphologic imaging was 97.3% and 99.1%, respectively. However, ⁶⁸Ga-PSMA HBED-CC PET detected LNM in 53 of 68 histopathologically proven metastatic LN fields (77.9%) whereas morphologic imaging was positive in only 18 of 67 (26.9%). ⁶⁸Ga- PSMA HBED-CC PET imaging performed significantly superior to morphologic imaging for detection of LNM (difference in the areas under the receiver-operating-characteristic curves, 0.139; 95% confidence interval, 0.063-0.214; P < 0.001). In 68Ga-PSMA HBED-CC PET, the mean size of PET-positive LN measured by CT or MRI was 8.3 ± 4.3 mm (range, 4-25 mm), and LNs, which were suspicious only in CT or MRI, presented with a mean size of 13.0 ± 4.9 mm (range, 8-25 mm). Conclusion: ⁶⁸Ga-PSMA HBED-CC PET imaging is a promising method for early detection of LNM in patients with biochemical recurrent prostate cancer. It is more accurate than morphologic imaging and thus might represent a valuable tool for guiding salvage lymphadenectomy.