Increased plasma d-2-hydroxyglutarate in isocitrate dehydrogenase 2–mutated blastic plasmacytoid dendritic cell neoplasm

SummaryBlastic plasmacytoid dendritic cell neoplasm is an exceedingly rare hematologic malignancy derived from the precursors of plasmacytoid dendritic cells. Mutations in isocitrate dehydrogenase (IDH) 1 and 2 genes have been discovered in a range of neoplasms including glioma, acute myeloid leukemia, chondrosarcoma, and intrahepatic cholangiocarcinoma. Mutant IDH acquires neomorphic enzymatic activity to generate the oncometabolite d-2-hydroxyglutarate (d-2HG). Here, we describe the first case of an IDH2 R140Q–mutated blastic plasmacytoid dendritic cell neoplasm in a patient with markedly elevated plasma d-2HG. This finding expands the spectrum of neoplasms with increased d-2HG in association with IDH mutation. The roles of IDH mutation and d-2HG in disease pathogenesis and assessment of clinical response are discussed.