Abstract: WANG Ya-zhe*, ZHANG Song, ZHENG Shu-ying, JIANG Bin, LIU Yan-rong, CHEN Shan-shan, LU Jin. *Peking University Institute of Hematology, Peking University People's Hospital, Beijing 100044, China Corresponding author: LU Jin, Email：jin1lu@sina.com 【Abstract】 A 19-year-old female presented with a dark erythematous maculopapule measuring 2 cm in diameter on the left lower limb for more than one year. Physical examination revealed an enlarged cherry-like lymph node in the right inguinal region． Histopathology of the lesion revealed that the normal structure of skin disappeared absolutely, and there was a diffuse infiltrate of medium-sized lymphoid tumor cells with unclear nucleoli. Immunohistochemically, the tumor cells strongly expressed CD4, CD56 and CD123, and partially expressed terminal deoxynucleotidyl transferase （TdT）. Flow cytometric analysis of bone marrow aspirates showed that abnormal cells amounted to 59.9%, and were positive for CD123st （strong）, human leucocyte antigen-DRst （strong）, CD56, CD304 （blood dendritic cell antigen-4）, CD7, CD11b, CD33, CD36 and chemokine （C-X-C motif） receptor 4, CD13 （dim）, CD4 （partial） and CD117 （partial）. Transmission electron microscopy of bone marrow cells revealed that there were massive uniformly sized lymphoid cells with thick processes on cell surfaces, a high nucleus/cytoplasm ratio, centrally located round nuclei occasionally with deep gyrus-like notches, clumped marginated heterochromatin and multiple nucleoli. Moreover, a small amount of cytoplasm was observed in the lymphoid cells with the presence of mitochondria and endoplasmic reticulum arranged in concentric circles, which were characteristic of plasma cells. The features of both dendritic cells and plasma cells were found in the tumor cells through transmission electron microscopy. Based on the above findings, a diagnosis of blastic plasmacytoid dendritic cell neoplasm （BPDCN） was made. 【Key words】 Leukemia, myeloid; Dendritic cells; Plasma cells

Key words: dendritic cells, Plasma cell