The Added Value of 18 F‐FDG PET/CT in Children With Langerhans Cell Histiocytosis Presenting as a Clinically Isolated Lesion

ABSTRACT Background The clinical utility of 18 F‐FDG PET/CT in children diagnosed with Langerhans cell histiocytosis (LCH) who present with a clinically isolated lesion remains unclear. This study aimed to assess the added value of 18 F‐FDG PET/CT in identifying occult lesions and assessing its impact on disease classification and clinical outcomes in this patient population. Methods This retrospective study included children who underwent surgical resection of a clinically isolated lesion, were confirmed to have LCH by histopathology, and received 18 F‐FDG PET/CT prior to initiation of systemic therapy. Outcomes including detection of additional lesions, disease reclassification, and progression‐free survival were analyzed. Kaplan–Meier analysis with log‐rank test was used to compare progression‐free survival between groups. Results A total of 44 children were included (median age 4.29 years; 70.5% male). 18 F‐FDG PET/CT identified additional lesions in 24 patients (54.5%), leading to reclassification as single‐system multifocal disease in 10 (22.7%) and multisystem disease in 14 (31.8%). Four patients (9.1%) had risk organ involvement. 18 F‐FDG PET/CT findings altered the treatment strategy in 54.5% of patients. All 5 relapsed patients belonged to the group with additional lesions ( p = 0.044). Conclusion 18 F‐FDG PET/CT detected additional lesions in over half of the children diagnosed with LCH presenting as a clinically isolated lesion, resulting in disease reclassification and improved risk stratification. 18 F‐FDG PET/CT should be routinely performed in this clinical scenario to ensure accurate staging and appropriate treatment.