Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare aggressive hematological malignancy arising from the precursors of plasmacytoid dendritic cells (professional type 1 interferon producing cells). Mature plasmacytoid dendritic cells share the common ancestor with Langerhans dendritic cells and interdigitating dendritic cells and are all arising from a CD34 positive myeloid stem cell. In vitro studies show that the precursor cells can be differentiated to plasmacytoid dendritic cells (PDC) upon IL-3 and CD40-L exposure. Not surprisingly, IL-3 receptor α (CD123) is a characteristic surface marker that distinguishes PDC from other macrophages and dendritic cell subtypes. Of note, follicular dendritic cells arise from mesenchymal stem cells (CD21 positive, CD35 positive) [1-2].