Blastic Plasmacytoid Dendritic Cell Neoplasm: Report of Three Cases.
Authors: Carluccio Paola , Delia Mario , Mestice Anna , Pastore Domenico , Ricco Alessandra , Giordano Annamaria , Perrone Tommasina , Gaudio Francesco , Liso Vincenzo , Specchia Giorgina 
Published: October 2019

Abstract
Abstract 4703
The World Health Organization (WHO) recently published a revised, updated edition of the WHO Classification of Tumours of the Haematopoietic and Lymphoid Tissues, including new criteria for the recognition of some previously described neoplasms as well as clarification and refinement of the defining criteria for others. It also adds entities – some defined mainly by genetic and immunophenotypic features – that have only recently been characterized. Particularly, the diagnosis and classification of acute leukemias of ambiguous lineage is debated; among these: “blastic NK-cell lymphoma” and “agranular CD4+/CD56+ hematodermic neoplasms”. Both of them are now known to be, in virtually all cases, a tumor derived from precursors of a specialized subset of dendritic cells, plasmacytoid dendritic cells, and so are myeloid-related neoplasms defined as blastic plasmacytoid dendritic cell neoplasm (BPDCN). This is a clinically aggressive neoplasm that is usually characterized at onset by solitary or multiple skin lesions, often with associated regional lymphadenopathy, and frequently by involvement of the PB and BM. Leukemic cells show submembranous cytoplasmic vacuoles and pseudopodia-like extensions of agranular cytoplasm. The blasts in such cases do not express myeloperoxidase or nonspecific esterase, and are characterized by the expression of CD4, CD43, CD56, CD123, BDCA-2/CD303, TCL1, and CLA; CD7 and CD33 are not uncommonly expressed as well, and TdT is expressed in about 30% of cases. There is no expression of CD34 or CD117. Here we report three cases with clinical data, cytological and immunophenotypic findings strongly suggesting the diagnosis of BPDCN.

Case 1
An 80 year-old-man was admitted to our institution on December 2006. He referred the occurrence of skin lesions since January 2005, when a diagnosis of extranodal B-cell non-Hodgkin lymphoma was made and treatment with conventional chemotherapy was performed, but without achieving any response. At our evaluation he presented leukocytosis (144 × 109/L) associated with purplish, firm nodules on the trunk, arms and face. Peripheral blood and bone marrow aspirate showed the presence of blast cells with a lymphoid appearance, granular periodic acid-Schiff (PAS) positivity and a high expression of CD33, CD4, and CD56. He was treated with AML-like therapy, but died of disease progression.

Case 2
A 79-year old woman was admitted in December 2006 with a 2-month history of anemia, splenomegaly, and weight loss of 10 kg in the last year. Laboratory tests were as follows: Hb, 41 g/L; leukocytes, 2.5 × 109/L (with 10% of blast cells); platelets, 43 × 109/L. No lymphadenopathy or skin lesions were present. Bone marrow examination revealed 41% of small to medium-sized blast cells without Auer rods or granula and negative reactivity to myeloperoxidase, esterase and PAS. She was treated with an AML-like protocol; she achieved partial response, but died after three months, of disease progression.

Case 3
A 69-year-old man was admitted to our Institution for cytopenia in June 2009. He referred the occurrence of brownish-purple firm nodules on the trunk since April 2009. At our evaluation he presented pancytopenia; bone marrow aspiration was performed and revealed infiltration by 65% of blasts with reticulated chromatin, evident nucleoli, a vacuolated cytoplasm and pseudopodia-like expansions. The blasts were negative for myeloperoxidase, monocyte esterase and PAS staining. Skin biopsy revealed a dermal infiltration by the same blastic-cell BM population. He underwent AML-like therapy and, although the skin lesions disappeared, 30% blastic bone marrow infiltration persisted.
Morphological revision of these cases, selected for their peculiar immunophenotype reported in the following Table, revealed the same cytological features and cytochemical reactivity in cases 2 and 3; case 1 had a lymphoblastic-like morphology and showed PAS positivity, but the lack of cCD3 was not consistent with the diagnosis of ALL. All the cases were FLT3-ITD+. We suggest that a correct modern panel of MoAb with a careful morphological examination could help to pose the diagnosis of BPDCN, which typically affects older patients and is characterized by poor prognosis.

Disclosures:
No relevant conflicts of interest to declare.