Introduction
Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with dismal prognosis. With difficulty in diagnosis, BPDCN was used in the 2008 World Health Organization (WHO) classification for the first time and became a distinct entity in 2016 WHO classification [1]. Recently, the presence of four out of five characteristic markers of BPDCN, namely, CD4, CD56, CD123, CD303, and TCL1, has been shown to aid in the accurate diagnosis of BPDCN [2]. Skin lesions commonly occur in a majority of patients with BPDCN, and blasts of BPDCN are suggested to arise from pre-malignant hematopoietic precursor clones [3]. Thus, patients with systemic lesions were treated with conventional chemotherapies for acute lymphoblastic leukemia, acute myeloid leukemia, or non-Hodgkin’s lymphoma, sometimes followed by autologous or allogeneic hematopoietic cell transplantation as a consolidation therapy [4]. However, its clinical and biological heterogeneous characteristics make its clinical management difficult [5]. Herein, we describe the case of a patient who suddenly developed leukemic form of BPDCN accompanied with CALReticulin (CALR ) mutation arising from myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T) without cutaneous lesion, showing severe tumor lysis syndrome (TLS) immediately after the induction therapy.