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Skin lesions in a patient with blastic plasmacytoid dendritic cell neoplasm

A 42-year-old man presented with a 5-month history of skin lesions, consisting of brown, rounded masses of variable size, which had quickly progressed over 2 weeks (left). Physical examination also showed a 2 cm lymph node in the right axilla. Blood analysis showed leucopenia as the sole abnormality. A skin biopsy showed diffuse dermal infiltration by medium-sized immature cells that expressed-cell HLA-DR, CD4, CD123 and CD25, with no expression of B-cell, T-cell or myeloid markers; the epidermis was not affected. A bone marrow aspirate showed 9% blast cells expressing CD123, CD4, CD303 and CD304. The final diagnosis was a blastic plasmacytoid dendritic cell neoplasm (BPDCN), affecting skin, bone marrow and lymph node (not biopsied). The skin lesions disappeared quickly after initiation of acute lymphoblastic leukaemia-type induction chemotherapy (right). After consolidation treatment, he underwent allogeneic stem cell transplantation (HSCT) from a matched unrelated donor and remains disease-free 2 years after the procedure. BPDCN is a rare subtype of acute leukaemia characterized by clonal proliferation of precursors of plasmacytoid dendritic cells. It shows aggressive behaviour and, despite initial response to chemotherapy, all patients eventually relapse. Allogeneic HSCT can provide durable responses and may be the most effective therapeutic option for eligible patients.