Acute myelomonocytic leukemia presenting as CD4+/CD56+ blastic plasmacytoid dendritic cell neoplasm

Blastic dendritic plasmacytoid cell neoplasm is a rare aggressive tumor of plasmacytoid dendritic cells. We report a 38-year-old female with nodular skin lesions on both legs at presentation which on immunohistochemical staining were CD4+ and CD56+ responding to blastic plasmacytoid dendritic cell neoplasm. Five months later the bone marrow analysis showed infiltration with 80% blasts which on flowcytometry had the immunophenotype suggesting acute myelomonocytic leukemia. Additional staining of skin lesions with CD123 was negative excluding blastic dendritic plasmacytoid cell neoplasm and suggesting the diagnosis of leukemia cutis. The patient achieved a complete remission after first course of standard induction chemotherapy, but relapsed 2 months later with leukemic manifestations and skin lesions. She died 13 months after initial diagnosis. This case illustrates the significance of immunophenotyping in differential diagnosis of blastic plasmacytoid dendritic cell neoplasm and myeloid leukemia cutis.   Key words: CD4+/CD56+ blastic plasmacytoid dendritic cell neoplasm, leukemia cutis, acute myelomonocytic leukemia, immunohistochemistry.