Diagnosis and prognostic role of 18F-FDG PET/CT for sarcomatoid differentiation renal cell carcinoma

Introduction: Sarcomatoid differentiation renal cell carcinoma (SDRCC) is a specific type of renal cell carcinoma, which is often aggressive and more likely to present as locally advanced or metastatic lesions than non-sarcomatoid differentiation renal cell carcinoma (non-SDRCC). ¹⁸F-FDG PET/CT can be used to evaluate tumor characteristics and metastatic status of RCC and predict its prognosis by measuring metabolic parameters such as the maximum standardized uptake value (SUVmax). Therefore, the aim of this study was to evaluate the diagnostic and prognostic performance of ¹⁸F-FDG PET/CT for SDRCC.

Methods: This retrospective study assessed newly diagnosed SDRCC patients staged with ¹⁸F-FDG-PET/CT, categorizing sarcomatoid differentiation into high-grade (HG-SDRCC) and low-grade (LG-SDRCC) based on a > 50% threshold, and compared their characteristics with a G3/G4 non-SDRCC control group. SUVmax, the mean standardized uptake value (SUVmean), metabolic tumor volume (MTV) and the total lesion glycolysis (TLG) were compared among HG-SDRCC, LG-SDRCC and non-SDRCC groups, and receiver operating characteristic (ROC) curves were analyzed for the optimal cutoff value and area under the curve (AUC). Patients with SDRCC were retrospectively followed up to analyze their overall survival (OS) and progression-free survival (PFS), and Kaplan-Meier curves, the log-rank test and the multivariate Cox proportional hazards analyses was performed to compare the survival rates and identify the prognostic factors.

Results: The SUVmax (P = 0.0027), MTV (P = 0.0299) and TLG (P = 0.0109) was significantly higher in SDRCC (n = 40) than in non-SDRCC (n = 128), while the SUVmean was not significantly different between SDRCC and non-SDRCC (P = 0.5801). And ROC shows AUC of SUVmax (AUC = 0.6561), MTV (AUC = 0.6137) and TLG (AUC = 0.6330) for SDRCC and non-SDRCC. Meanwhile, the SUVmax (P = 0.0004), MTV (P = 0.0414) and TLG (P = 0.0126) was significantly higher in HG-SDRCC (n = 21) than in non-SDRCC, while the SUVmax, MTV and TLG was not significantly different between LG-SDRCC (n = 19) and non-SDRCC. ROC shows AUC of SUVmax (AUC = 0.7364), MTV (AUC = 0.6388) and TLG (AUC = 0.6689) for HG-SDRCC and non-SDRCC. The log-rank test shows SUVmax > 11 (PFS: HR = 2.554(1.042-6.262), P = 0.0404; OS: HR = 3.542 (1.366-9.186) P = 0.0093). Multivariate Cox proportional hazards analyses show SUVmax > 11 (PFS: HR = 2.196 (0.989-4.878), P = 0.053; OS: HR = 3.445 (1.192-9.955), P = 0.022) and TLG > 500 (PFS: HR = 2.281 (1.003-5.187), P = 0.049) were still risk factors under the mixing of age and gender.

Conclusions: The metabolic parameters of ¹⁸F-FDG PET/CT including SUVmax, MTV and TLG could be effectively utilized for the diagnosis and prognosis of SDRCC.

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