Early plasmacytoid dendritic cell leukemia/lymphoma coexpressing myeloid antigenes

Early plasmacytoid dendritic cell (pDC) leukemia/lymphoma has recently been described as a CD4⁺CD56⁺ lineage negative malignancy with characteristic clinical, morphologic, immunophenotypic, and biological features. We present a case of a 72-year-old man who was diagnosed with isolated skin involvement 30 months ago and received numerous chemotherapy cycles that did not prevent three relapses of the disease, the last two involving the bone marrow. The bone marrow was nearly completely infiltrated with small- to medium-sized blasts displaying a high nuclear to cytoplasmic ratio, a cytoplasm with faint basophilia lacking granulations or Auer rods. Small vacuoles surrounding the nucleus were frequently observed. Flow cytometry showed CD4⁺, CD56⁺, CD45⁺, CD38⁺, HLA-DR⁺, CD33⁺, CD123⁺, CD2⁻, cyCD3⁻, CD7⁻, CD10⁻, CD11b⁻, CD13⁻, CD14⁻, CD16⁻, CD19⁻, cyCD22⁻, CD24⁻, CD34⁻, CD57⁻, CD61⁻, CD64⁻, CD65⁻, cyCD79a⁻, CD117⁻, MPO⁻, and TdT⁻ population. At the second bone marrow relapse, CD117 was also positive. Our patient was initially treated with acute myeloid leukemia-type chemotherapy, later he was given acute lymphoblastic leukemia-type treatment, and at the last relapse he received CHOP chemotherapy. Each treatment led to rapid response of tumor manifestations with disease-free intervals of 7 months, 9 months, and 8 months, respectively. Although patients usually have an ominous prognosis, with only 25% living more than 24 months, our patient is alive after 30+ months and has again achieved complete remission after the last chemotherapy.