Erdheim-Chester disease (ECD) is a rare, potentially fatal multiorgan myeloid neoplasm occurring mainly in adults. The diagnosis is established by clinical, radiologic, and histologic findings; ECD tumors contain foamy macrophages that are CD681, CD1631, CD1a2, and frequently S1002. The purpose of this report is to describe the clinical and molecular variability of ECD. Between 2011 and 2015, 60 consecutive ECD patients (45 males, 15 females) were prospectively evaluated at the National Institutes of Health Clinical Center. Comprehensive imaging and laboratory studies were performed, and tissues were examined for BRAF V600E and MAPK pathway mutations. Mean age at first manifestations of ECD was 46 years; a diagnosis was established, on average, 4.2 years after initial presentation. Bone was the most common tissue affected, with osteosclerosis in 95% of patients. Other manifestations observed in one-third to two-thirds of patients included cardiac mass and periaortic involvement, diabetes insipidus, retro-orbital infiltration, retroperitoneal, lung, central nervous system, skin, and xanthelasma, affecting patients in variable ways. Methods of detection included imaging studies of various modalities. Mutation in BRAF V600E was detected in 51% of 57 biopsy specimens. One patient had an ARAF D228V mutation, and 1 patient had an activating ALK fusion. Treatments included interferon a, imatinib, anakinra, cladribine, vemurafenib, and dabrafenib with trametinib; 11 patients received no therapy. The diagnosis of ECD is elusive because of the rarity and varied presentations of the disorder. Identification of BRAF and other MAPK pathway mutations in biopsy specimens improves ECD diagnosis, allows for development of targeted treatments, and demonstrates that ECD is a neoplastic disorder. This study was registered at www.clinicaltrials.gov as #NCT01417520.
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