Early Dynamic 18F-FDG PET/CT SUVmax and Its Association with Pathological Stage and Tumor Grade in Bladder Cancer: A Prospective Exploratory Study

Background and Objectives: Accurate preoperative staging and grade assessment are crucial for optimal treatment selection in bladder cancer. This prospective study evaluated multi-timepoint Fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) imaging for predicting pathological stage and tumor grade. Materials and Methods: Seventy-two patients with bladder carcinoma underwent 18F-FDG PET/CT including early dynamic (0–2, 2–4, 8–10 min), standard (60 min), and late (~120 min) imaging following a standardized furosemide hydration protocol. Maximum standardized uptake values (SUVmax) were correlated with histopathological findings. Diagnostic performance was evaluated using receiver operating characteristic (ROC) curve analysis with Youden index for optimal cut-offs. Results: The cohort comprised 72 patients (84.7% male, mean age 64.8 ± 10.7 years) with pathological stages Ta (36.1%), CIS (15.3%), T1 (31.9%), and T2 (16.7%). High-grade tumors demonstrated significantly higher SUVmax at early dynamic imaging (0–2 min: 1.50 vs. 1.00, p = 0.028) and late imaging (11.40 vs. 9.50, p = 0.045) compared to low-grade tumors. Early dynamic imaging at 0–2 min achieved the highest, although modest, diagnostic performance for high-grade prediction (area under the curve (AUC) = 0.652) and muscle-invasive disease prediction (AUC = 0.669), with optimal cut-offs of SUVmax = 1.40 and 1.80, respectively. Early dynamic SUVmax correlated significantly with tumor grade (ρ = 0.261, p = 0.027) and tumor size (ρ = 0.424, p < 0.001). The negative predictive value for muscle-invasive disease was 90.4%, but sensitivity was only 58.3%. Conclusions: Early dynamic 18F-FDG PET/CT imaging at 0–2 min showed the highest, although modest, diagnostic performance among the evaluated time points for predicting tumor grade and muscle invasion. The identified SUVmax cut-offs are exploratory and require external validation in larger multicenter studies before clinical use. Trial registration: Not registered.