Erdheim-Chester Disease with BRAF V600E Mutation and a Concomitant Myeloid Malignancy Sharing NRAS and IDH2 Mutations.

Erdheim-Chester disease (ECD) is a rare clonal histiocytic process that is characterized by a foamy (xanthomatous) proliferation often associated with Touton giant cells. The diagnosis is often challenging and not exclusively a histologic diagnosis, as it requires correlation with unique clinical, radiographic and recently described molecular findings. Activating mutations involving the MAPK pathway including BRAF, ARAF, N/KRAS and MEK are recurrent in the disease. However, it is increasingly being described that mutations associated with clonal hematopoiesis are also found in bone marrow specimens of patients with Erdheim-Chester disease (ECD), as well as higher frequency of overt concomitant myeloid malignancy including acute myeloid leukemia, myeloproliferative neoplasms, myelodysplastic syndromes, and mixed myeloproliferative neoplasms/myelodysplastic syndromes. Herein, we report a unique case of a patient presenting with BRAF-V600E-positive ECD with with peripheral blood findings consistent with a concurrent myeloid malignancy featuring co-occurrence of NRAS and IDH-2 mutations.