Clinico-Pathologic Features of Adult Erdheim–Chester Disease in South Korea: A Multicenter Retrospective Study (KCSG LY22-15)

PurposeErdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis characterized by heterogeneous multisystem manifestations and frequent MAPK-ERK pathway alterations.Data on the clinico-pathologic features and real-world outcomes of adult ECD in South Korea are limited. Materials and MethodsWe conducted a retrospective multicenter cohort study of adult patients (≥18 years) with ECD at seven Korean Cancer Study Group (KCSG)-affiliated institutions between October 2008 and June 2024.Clinical and pathologic features, BRAF V600E mutation status, treatment patterns, and overall survival (OS) were analyzed using the Kaplan-Meier method. ResultsTwenty-two patients were included (median age 57 years [IQR 45-64]; 50% male).Organ involvement was heterogeneous: bone (54.5%), retroperitoneal/renal (31.8%), central nervous system (27.3%),cardiovascular (27.3%), hypothalamic-pituitary axis (27.3%), pulmonary (18.2%), and skin (13.6%); multisystem disease (≥2 organs) was present in 40.9%.BRAF V600E was positive in 11 of 19 tested patients (57.9%).Systemic treatment was initiated in 18 patients (81.8%); interferon-α-based regimens were the most common first-line approach (50.0%).Among 16 evaluable patients, the disease control rate (CR/PR/SD) was 87.5%.With a median follow-up of 4.6 years (IQR 1.3-6.5),2-and 5-year OS rates were 90.0% and 74.3%, respectively. ConclusionKorean adult patients with ECD demonstrate heterogeneous organ involvement and frequent BRAF V600E positivity.Real-world treatment remains dominated by interferon-α-based approaches,