Prognostic impact of risk organ involvement and metabolic parameters assessed by staging 18F-FDG PET/CT in pediatric Langerhans cell histiocytosis.

OBJECTIVE: To investigate the prognostic impact of risk organ involvement and baseline metabolic activity assessed by staging 18F-fluorodeoxyglucose (FDG) PET/computed tomography (CT) in newly diagnosed pediatric Langerhans cell histiocytosis (LCH). METHODS: Thirty-two children with histologically confirmed LCH who underwent baseline 18F-FDG PET/CT were retrospectively analyzed. Age, disease extent (single-system vs. multisystem), risk organ involvement (RO- vs. RO+), and baseline metabolic parameters [maximum standardized uptake value (SUVmax), SUVmean, metabolic tumor volume, total lesion glycolysis (TLG), and tumor-to-background ratio (TBR)] were evaluated for their association with progression or relapse. Optimal cut-offs were derived from receiver operating characteristic analysis (Youden index). Survival outcomes were analyzed using Kaplan-Meier and Cox regression models. RESULTS: Over a median follow-up of 33 months, disease progression or relapse occurred in 13 patients (40.6%) and was significantly associated with younger age (P = 0.040), higher SUVmax (P = 0.016), higher TBR (P = 0.007), and TLG (P = 0.033), multisystem LCH (P = 0.004), and risk organ positivity (P < 0.001). Risk-organ involvement was the strongest univariate predictor of adverse outcome (hazard ratio: 14.9, 95% confidence interval: 3.3-67; P < 0.001). CONCLUSION: Baseline 18F-FDG PET/CT provides important prognostic information in pediatric LCH, with risk organ involvement emerging as the strongest univariate prognostic factor in this cohort, supporting its role in early risk stratification, suggesting a potential role in future risk-adapted treatment planning. Higher SUVmax, TBR, and TLG were associated with progression/relapse in group comparisons, whereas only SUVmax and TBR were significantly associated with progression-free survival in univariate Cox analysis.