LAUSR

A 74-year-old patient was hospitalised for the investigation of generalised lymphadenopathy and cutaneous manifestations (red and inflammatory nodules, erythema in 12 different localizations) 2 years after a diagnosis of chronic myelomonocytic leukaemia (CMML)-1 with a normal karyotype. Blood counts showed persistent monocytosis and thrombocytopenia (haemoglobin concentration 160 g/l, leucocytes 7 04 9 10/l, monocytes 2 13 9 10/l, platelets 81 9 10/l). The immunophenotypic profile of monocytes in the peripheral blood showed an accumulation of classical monocytes CD14/CD16 (MO1, 96 76%, top left), consistent with the previous diagnosis of CMML (Selimoglu-Buet et al, 2015). In addition to the expected increased monocytes and dysplastic features, bone marrow examination showed typical cells of blastic plasmacytoid dendritic cell neoplasm (BPDCN) (May– Gr€ unwald–Giemsa stain, 9100, top right). Flow cytometry confirmed the nature of the BPDCN cells (3%) with a typical profile, CD45, CD4, CD56, CD123, HLA-DR, CD2, CD33, CD34 and CD117 , and revealed aberrant CD56 expression by monocytes. We compared the expression of multiple differentiation markers by monocytes and BPDCN cells using a radar plot (Kaluza software, Beckman-Coulter , monocytes in green, BPDCN cells in blue, bottom left and right). This revealed two phenotypically distinct populations. The karyotype was again normal. BPDCN was also confirmed by histological examination and immunohistochemistry of skin lesions and lymph node biopsy specimens. A diagnosis of BPDCN associated with CMML-1 was made. Azacitidine treatment was recommended because of the age of the patient and high toxicity of conventional BPDCN treatment. BPDCN is a rare haematological malignancy that is associated with myeloid neoplasms in 10–20% of patients.