Monocytosis and Clonal Hematopoiesis in Peripheral Blood as Indicators of Myeloid Neoplasm in Erdheim-Chester Disease

BACKGROUND: Erdheim-Chester disease (ECD) is a rare non-Langerhans histiocytosis, with ~10% of cases showing myeloid neoplasms (MNs). METHODS: A 70-year-old woman with cardiac arrhythmia and right atrial mass was diagnosed with ECD by biopsy. Complete blood count showed persistent monocytosis. Targeted next-generation sequencing (NGS) of peripheral blood (PB) for evaluating clonal hematopoiesis (CH) was performed. RESULTS: The NGS revealed ASXL1 Asn893Cysfs*12 (variant allele frequency [VAF]: 37.2%), TET2 His1031 Glnfs*11 (VAF: 49.0%) and TET2 Tyr1255* (VAF: 47.5%). Bone marrow examination confirmed concomitant chronic myelomonocytic leukemia. CONCLUSIONS: NGS using PB needs to be considered in ECD for the detection of CH and for the diagnosis of coexisting MNs.