Prognostic Value of O-(2-¹⁸F-Fluoroethyl)-l-Tyrosine PET for Patients with Recurrent Glioblastoma

The determination of prognoses for patients with recurrent glioblastoma remains challenging. This study aimed to evaluate the prognostic value of static O-(2-¹⁸F-fluoroethyl)-l-tyrosine (¹⁸F-FET) PET parameters in patients with recurrent glioblastoma. Methods: We retrospectively evaluated patients treated in 3 institutional clinical trials examining vascular endothelial growth factor inhibition, immune checkpoint inhibition, or their combination in recurrent glioblastoma. Patients with a baseline ¹⁸F-FET PET were included in the analysis and stratified by treatment group. Prognostic value was evaluated using univariate Kaplan-Meier and multivariate Cox regression analyses, with receiver-operating-characteristic analysis to identify optimal thresholds. Results: Both univariate and multivariate analysis revealed that patients with a larger baseline metabolic tumor volume (MTV) and higher mean tumor-to-background ratio (TBR_mean) had an increased risk of death independent of treatment (MTV per 10 mL: hazard ratio, 1.06; 95% CI, 1.01-1.12; P = 0.023; TBR_mean: hazard ratio, 1.91; 95% CI, 1.14-3.21; P = 0.014). Receiver-operating-characteristic analysis showed that an MTV and TBR_mean of more than 27.94 cm³ and 2.15, respectively, identified patients with worse overall survival in our patient population. Conclusion: Pretreatment MTV and TBR_mean had a significant prognostic value in patients with recurrent glioblastoma, independent of treatment, and could be useful to stratify and select patients for future clinical trials.