Unraveling the Genetic Landscape of Langerhans Cell Histiocytosis in Korean Patients: Comprehensive Insights from Mutational Profiles and Clinical Correlations.
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PURPOSE: This study aimed to conduct a comprehensive genetic analysis of patients with Langerhans cell histiocytosis (LCH), focusing on the frequency of mitogen-activated protein kinase (MAPK) pathway mutations, detailed mutation profiles of MAPK pathway genes, and their correlation with clinical features and prognosis in Korean LCH patients. MATERIALS AND METHODS: We performed targeted next-generation sequencing, capable of capturing exons from 382 cancer-related genes, on genomic DNA extracted from formaldehyde-fixed and paraffin-embedded samples of 45 pathologically confirmed LCH patients. RESULTS: The majority of patients (91.1%) exhibited single-system disease, with bone being the most common location (84.4%). Initial treatments varied, and no patients died during a median follow-up of 6.8 years. Our genetic assays revealed that all patients had MAPK pathway alterations, including BRAF mutations in 51.2%, MAP2K1 mutations in 42.2%, RAF1 mutations in 4.4%, and a KRAS mutation in 2.2%. These mutations were mutually exclusive. Detailed mutation profiles indicated that among the BRAF mutations, there were 18 point mutations and five in-frame deletions, while most MAP2K1 mutations were in-frame deletions, with only one missense mutation. We detected previously unreported variations of point mutations in BRAF, MAP2K1, KRAS, and the first instance of a RAF1-KLC1 fusion in LCH. MAP2K1 mutations occurred more frequently in older patients, whereas BRAF V600 mutations were commonly associated with unifocal bone disease. Genetic mutations did not correlate with high-risk features or event-free survival. CONCLUSION: This study identified mutually exclusive MAPK pathway mutations in every LCH patient through comprehensive genetic analysis, highlighting the importance of inclusive testing in understanding the disease's genetics.