Introduction
Juvenile xanthogranuloma (JXG) is classified as a histiocytosis that is generally diagnosed on the basis of the presence of cutaneous nodules in infancy. It has been considered benign and could undergo spontaneous regression without therapy.1 However, some patients with systemic JXG, particularly patients with central nervous system (CNS) involvement, might have severe neurological sequelae.2 Conventional chemotherapy based on Langerhans cell histiocytosis (LCH) have been applied for these severe cases,2 but the response rate remains unclear. In addition, adverse events and late complications induced by anticancer drugs should be avoided in paediatric patients as much as possible, especially in neonates. Recently, BRAF V600E mutation and recurrent kinase fusions, including BRAF, NTRK and anaplastic lymphoma kinase (ALK), including KIF5B-ALK fusion, have been identified in histiocytic neoplasms.3,4. We present the case of a patient with systemic JXG with KIF5B-ALK fusion detected by next-generation sequencing (NGS) panel -based comprehensive genome profiling (CGP) for solid tumours, in whom CNS lesions had caused neurological disorders. There has been no report about ALK inhibitor for an infant case of histiocytosis.