¹⁸F-FDG PET/CT in pediatric langerhans cell histiocytosis: relation to BRAF^v600e mutation and risk stratification

BRAF^V600E correlates with high-risk features and poor response to chemotherapy in pediatric Langerhans cell histiocytosis (LCH). This study aimed to evaluate the role of ¹⁸F-FDG PET/CT in risk stratification and to explore the relationship between ¹⁸F-FDG uptake and BRAF^V600E mutation in LCH.

Pretreatment ¹⁸F-FDG PET/CT scans from 114 newly diagnosed pediatric LCH were retrospectively analyzed. The associations between imaging findings and clinico-pathological parameters were investigated.

PET/CT imaging led to a change of disease stratification in 47 (41.2 %) patients. The most common additional organs detected by PET/CT were lymph nodes and thymus. Elevated C-reactive protein (CRP) levels were associated with upstaging [Odds ratio (OR): 2.737, 95 % confidence interval (CI): 1.193-6.276, p = 0.017]. LCH lesions showed significantly higher SUVmax in patients with elevated CRP levels compared to those with normal levels (10.2 ± 4.7 vs. 7.3 ± 3.6, p = 0.001). BRAF^V600E status was tested in 70 patients. Lower ¹⁸F-FDG uptake (SUVmax: 8.2 ± 3.3 vs. 10.8 ± 4.9, p = 0.019) was observed in mutated-BRAF^V600E. Multivariate logistic regression analysis revealed that SUVmax ≤ 10.6 (OR: 6.868, 95 % CI: 1.751-26.946, p = 0.006), absence of thymus involvement (OR: 11.849, 95 %CI: 1.907-73.635, p = 0.008) and CRP ≥ 15.0 mg/L (OR: 8.062, 95 % CI: 1.538-42.263, p = 0.014) significantly correlated with BRAF^V600E mutation.

PET/CT identifies extra-osseous diseases in about 40% of patients, especially those with elevated CRP levels. Moreover, ¹⁸F-FDG PET/CT findings were significantly associated with BRAF^V600E mutation status, although wide CIs warrant cautious interpretation.