Characterization of tumor thrombus in renal cell carcinoma with prostate specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT).

INTRODUCTION: Venous tumor thrombus (TT) occurs as part of the natural history of renal cell carcinoma (RCC) local progression in a small minority of cases. MRI is currently the most accurate imaging modality for determining TT extent. PSMA PET/CT may improve RCC staging and IVC TT characterization. The objective of this study was to investigate the role of PSMA PET/CT in defining superior extent of TT in RCC and TT IVC tributary vessel spread, with comparative accuracy vs. MRI, to assess suitability for resection and inform preoperative surgical planning. METHODS: Patients who underwent PSMA PET/CT for assessment of renal malignancy with TT from 2015 to 2020 at 3 tertiary hospitals in Brisbane, Australia, were retrospectively identified. TT extent was classified using Mayo Clinic levels and compared according to imaging modality. RESULTS: Fourteen patients were included, all of which were clear cell RCC. Ten patients also underwent MRI, 6 of which were concordant in extent according to MRI and PSMA PET. Discordant extent occurred in 4 patients, of which 2 patients had non-PSMA avid thrombus (Mayo level 0 and level 3 on MRI). Further discordance was seen in a patient with adrenal vein and lumbar vein TT only seen on MRI and PSMA PET/CT, respectively. Finally, discordant extent was seen in another patient with Mayo level 4 TT without lumbar vein involvement on MRI vs. level 3 on PSMA PET/CT with lumbar vein involvement. CONCLUSIONS: PSMA PET/CT can provide additional information about TT extent in RCC which may not be seen on MRI. Additional information from PSMA PET/CT in this setting may assist surgical planning, in addition to detection of metastatic disease.

The role of dual tracer PSMA and FDG PET/CT in renal cell carcinoma (RCC) compared to conventional imaging: A multi-institutional case series with intra-individual comparison.

PURPOSE: The objective of this study was to perform an intra-individual dual tracer comparison of Fluorodeoxyglucose (FDG) and Prostate Specific Membrane Antigen (PSMA) computed tomography (CT)/Positron Emission Tomography (PET) against standard of care (SOC) imaging for the characterisation, staging and restaging of renal cell carcinoma (RCC). METHODS: A multicentre retrospective cohort study was performed at 3 major tertiary referral institutions in Brisbane, Australia between 2015 and 2020. All patients who underwent both PSMA and FDG PET/CT following SOC imaging for investigation of RCC were identified. Clinical details, imaging characteristics and histopathology were collected prior to univariate statistical analysis. RESULTS: Eleven patients who underwent dual tracer PET/CT were included. Mean age was 65.5 years (SD 8.8). Most patients were male (64%) with clear cell morphology (91%). The indication for dual tracer PET was staging (36%) and restaging after radical/partial nephrectomy (64%). Primary tumour assessment showed mixed avidity patterns (concordant 40%, discordant favouring PSMA 20%, and FDG 40%). Metastatic disease assessment showed concordant avidity in 6 patients (55%), concordant negative in 3 (27%), and discordant uptake favouring PSMA. PET outperformed SOC imaging for assessment of metastatic disease in 5 patients (45%) and equivalent for the remainder. A change in management was noted in three cases (27%). CONCLUSION: Dual tracer FDG and PSMA PET/CT for assessment of primary and metastatic RCC were mostly concordant. PET imaging outperformed conventional imaging and led to a change in management for 1 in 4 patients. Further studies with larger samples sizes are required to validate these findings and identify characteristics to guide patient selection for selective or dual tracer use.