An aggressive immature hematologic neoplasm formerly known as blastic NK cell lymphoma, composed of cells with a lymphoblast-like morphology. Recent evidence suggests derivation from a plasmacytoid monocyte. Patients present with cutaneous tumors and bone marrow involvement. The disease is CD4+/CD56+ hematodermic neoplasm (MONDO_0019467). Also known as: BPDCN, agranular CD4+ CD56+ hematodermic neoplasm/tumor, agranular CD4+ natural Killer cell leukaemia, agranular CD4+ natural Killer cell leukemia, blastic NK-cell lymphoma, blastic natural Killer leukemia/lymphoma, blastic plasmacytoid Dendritic cell neoplasm, blastic plasmacytoid dendritic cell neoplasm.