[Rare diagnosis of CD4+56+ leukemia from dendritic cells type DC2]

CD4+56+ hematodermic neoplasm or leukemia from early plasmocytoid dendritic cells type DC2 was recognized by WHO-EORTC classification of cutaneous lymphomas as a separate entity related to the plasmacytoid precursor dendritic cell (pDC). This diagnosis is based on expression of CD4 and CD56 antigens and absence of B, T or myeloid lineage markers. Immunohistochemistry and flow cytometry are the only methods, which allow identification of this disease, either in isolated skin lesions or in a leukemic form. Although the co-expression of CD4 and CD56 is rare and the number of described cases is low, this group bears similar characteristics in a clinical course of disease. It is a very aggressive leukemia/lymphoma, usually with primary skin involvement, in half of the cases infiltrating bone marrow or lymph nodes. Despite high rate of initial response to treatment, early and widespread relapses occur and patients die of disease progression. Although the physiological counterpart of tumour cells was identified, the origin of the disease is still discussed because of aberrant expression of cell markers. Optimal treatment is not known. However, this aggressive disease requires radical approach with intensive chemotherapy regimens, prophylaxis of CNS involvement and early indication of allogeneic bone marrow transplantation. Two case reports are described.