The associations among the glucose metabolic rate, tumor progression, and histopathological grade in metabolically active renal cell carcinoma: A comparison using whole-body 4D parametric FDG-PET/CT imaging

Objective: To investigate the associations among the tissue metabolic rate of ¹⁸ F-fluorodeoxyglucose (FDG), i.e., the MR _FDG value (mg/min/10 mL), tumor progression, and the histopathological grade in metabolically active renal cell carcinoma (RCC), using four-dimensional parametric FDG-positron emission tomography (PET)/computed tomography (CT) imaging. Methods: Dynamic whole-body FDG-PET/CT scans were performed for 28 patients newly diagnosed with RCC. We compared the obtained MR _FDG values with the patients' tumor size, T stage, presence/absence of metastasis and venous tumor thrombus (VTT), and histopathological grade based on the Fuhrman and World Health Organization/International Society of Urological Pathology classifications. Results: A total of 30 RCC lesions were analyzed. A strong positive correlation was observed between the MR _FDG values and tumor size (R=0.68, p<0.0001). The tumors at ≥T2 stage showed significantly higher MR _FDG values compared to the T1-stage tumors (8.30 ± 7.33 vs. 2.20 ± 1.44, p=0.003). The tumors with VTT had significantly higher MR _FDG values versus those without VTT (6.70 ± 5.39 vs. 3.38 ± 6.07, p=0.002), but the tumors showed similar MR _FDG values regardless of the presence/absence of metastasis (5.83 ± 4.57 vs. 4.65 ± 1.50, p=0.07). The Fuhrman G4 tumors showed significantly higher MR _FDG values versus the G1–3 tumors (11.05 ± 9.97 vs. 2.50 ± 2.67, p=0.03), although no significant differences were observed between the G1/2 and G3/4 tumors by either classification. Conclusions: High values of the MR _FDG in RCC reflected a high degree of local development and a high Fuhrman grade, but they did not reflect a propensity for metastasis.