AML-327: Plasmacytoid Dendritic Cell Proliferation Associated with Acute Myeloid Leukemia: A Case Report

Context: Plasmacytoid Dendritic Cells (pDCs) are hematopoietic, type 1 interferon-producing cells. Neoplastic expansion of these cells is very rare and is classified into two different malignancies: Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN) and mature pDC proliferation associated with myeloid neoplasia. Objective: We present here a diagnostically challenging case of pDC proliferation associated with AML, with an unusual occurrence in a young 26-year-old male. This patient achieved complete remission with an ALL-based chemotherapy regimen in combination with a Bcl-2 inhibitor. Patient Case Report: A 26-year-old man presented to our clinic with a 1-month history of weakness, malaise and myalgia. Blood counts and peripheral blood smear showed normocytic anemia (Hb 103 g/L) and leukopenia (WBC 2.4 x 103 μ/L) with dominant lymphocytosis, which progressed to severe leukopenia (WBC 0.8 x103 μ/L) and thrombocytopenia (PLT 18 x 103 μ/L) in two weeks. Bone marrow biopsy was performed, indicating metastatic nasopharyngeal carcinoma. He underwent detailed ORL examination, and except for nodular lymphoid tissue in the epipharynx, no other abnormalities were observed. Additionally, MRI of the neck showed normal findings. We did a second bone marrow biopsy with bone marrow aspiration. Immunophenotyping by flow cytometry showed 50% infiltration with cells with weak expression of CD45, no expression of CD34, co-expression of CD4/CD56, presence of HLADR/CD123, and expression of CD33, CD117, and cytoplasmic nTDT, suggesting BDPCN. The histological examination of the bone marrow confirmed the diagnosis, and the immunohistochemical staining excluded neoplasia of ectodermal origin. Still, the patient had no evident cutaneous lesions, organomegaly, nor lymphadenopathy. The bone marrow sample was sent for consultative opinion in a referent center, and based on the negativity of TCL1, the diagnosis of pDCS associated with AML was established. RUNX-1 mutation and other prognostic markers for AML, however, were not detected. The patient achieved complete remission with 2 cycles of Hyper-CVAD plus venetoclax and underwent stem cell transplantation. Conclusions: pDC-myeloid neoplasm should be considered as a differential diagnosis of BPDCN, and more extended immunohistochemical analysis is required for correct diagnosis.