Performance of⁶⁸Ga-PSMA-11 PET/CT for Diagnosing Tumor Thrombus and Predicting Response to Pembrolizumab and Axitinib in Patients with Renal Cell Carcinoma: A Pilot, Retrospective Study.

Abstract

ObjectivesTo investigate the performance of ⁶⁸Ga-PSMA-11 PET/CT for diagnosing tumor thrombus (TT) and predicting response to pembrolizumab and axitinib in renal cell carcinoma (RCC) with TT.MethodsWe reviewed RCC patients who underwent contrast-enhanced CT, mpMRI, and ⁶⁸Ga-PSMA-11 PET/CT. Diagnostic performance for detecting TT was analyzed, with TT confirmed by experienced pathologists. We further analyzed clear cell RCC (ccRCC) patients with TT who received pembrolizumab and axitinib and evaluated imaging features for predicting therapeutic efficacy by using receiver operating characteristic analysis. Internal validation was performed using bootstrap resampling (1000 iterations). Model calibration was assessed with the Hosmer-Lemeshow test.ResultsA total of 166 RCC patients were initially included, of whom 56 had TT. ⁶⁸Ga-PSMA-11 PET/CT showed higher overall diagnostic performance for TT than contrast-enhanced CT and mpMRI, with incremental detection primarily observed for Mayo level 0-I TT. The sensitivity and specificity of PET/CT in diagnosing TT were 0.96 (95% CI 0.88-0.99) and 0.97 (95% CI 0.92-0.99), respectively. Then, 35 ccRCC patients with TT underwent an average of 5 cycles of pembrolizumab and axitinib, followed by surgery. Following neoadjuvant therapy, 21 patients exhibited a partial response, while 14 showed nonresponse. TT SUVmax demonstrated significant predictive value for response to neoadjuvant therapy, with an AUC of 0.80 (95% CI 0.63-0.92; bootstrap-corrected, 0.79). The Hosmer-Lemeshow test indicated adequate calibration (P > 0.05).Conclusions⁶⁸Ga-PSMA-11 PET/CT may provide incremental value for detecting low-level TT and shows potential for predicting response to pembrolizumab plus axitinib in RCC. However, the clinical significance of detecting early TT remains uncertain.