Baseline Metabolic Tumor Volume Measured by FDG PET/CT Before Neoadjuvant Chemotherapy Predicts Survival in Pediatric Osteosarcoma

429 Objectives Initial baseline metabolic tumor volume (MTV) has been reported to be associated with metastasis free survival in osteosarcoma. The purpose of the study was to evaluate whether initial MTV and total lesion glycolysis (TLG) could be predictors of event free survival (EFS) and overall survival (OS) in osteosarcoma. Methods Thirty-four patients with osteosarcoma were enrolled who underwent baseline FDG PET/CT, neoadjuvant chemotherapy and subsequent surgical resection. Maximum and peak standardized uptake value (SUVmax, SUVpeak), MTV and TLG of the primary lesion were measured. MTV and TLG were measured using an absolute threshold of SUV 2.5, which best segmented the tumor volume from a range of methods (Figure 1). Histological response after tumor resection was evaluated and patients with over 90% tumor necrosis were considered as responders. EFS and OS were defined as the time interval from study enrollment to date of first event (EFS: recurrence, progression, death, OS: death from any cause), or to date of last contact for patients without events. Each PET parameter was compared between patients with and without recurrence, and also between dead and alive patients by Wilcoxon test. PET parameters were divided into two groups using an optimized cut-off, using the maximum Youden index from receiver operating characteristic (ROC) analysis. EFS/OS distributions between PET parameter groups were compared using the log-rank test. Cox regression analysis was done to study the association between individual PET parameters and EFS/OS after adjusting for histologic response and initial presence of metastasis. Results The 34 enrolled patients were followed up for a median of 3.6 years (range 1.4 to 5.3), with 15 recurrences and 10 deaths during this period. Nine patients had evidence of metastasis at initial diagnosis. Two patients received surgical resection at a different time point from the others, and thus were excluded for response evaluation. Initial MTV and TLG were significantly higher in patients with recurrence than those without recurrence (P = 0.01 and 0.006, respectively), while SUVmax and SUVpeak were not (P = 0.13, and 0.08). Initial SUVmax, SUVpeak, MTV and TLG were significantly higher in patients who died than survivors (P = 0.03, 0.03, 0.0006, and 0.0005). On univariate analysis, all initial PET parameters were associated with EFS and OS. Histologic response and initial presence of metastasis were associated with OS but not with EFS (Table 1, Figure 2). On multivariable Cox regression analysis using histologic response and initial presence of metastasis as covariates, initial MTV and TLG were independently associated with the EFS (P = 0.027 and 0.009) and OS (P = 0.014 and 0.011), while SUVmax was not associated with EFS (P = 0.06) nor OS (P = 0.16). SUVpeak was independently associated with EFS (P = 0.0001) but not with OS (P = 0.99). Conclusions Initial baseline tumor PET MTV and TLG are independent predictors of EFS and OS in pediatric patients with osteosarcoma. These intriguing findings need further validation in larger prospective studies. $$graphic_DF4D573F-430B-481C-B19E-7C2B58764DDC$$