Blastic plasmacytoid dendritic cell neoplasm: Report of a case with extracutaneous presentation and extensive bone marrow involvement

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare aggressive hematopoietic malignancy. The diagnosis of BPDCN is challenging owing to the lack of lineage-specific markers and confusing historic misnomers. A correct and timely diagnosis of BPDCN, however, has significant clinical impact because induction chemotherapy used for acute myeloid leukemia (AML) followed by stem cell transplant seems to improve the disease outcomes. Here, we report a case of BPDCN with unusual extracutaneous presentation and extensive bone marrow involvement. The patient was a 68-year-old woman found to have pancytopenia and diffuse lymphadenopathy. Peripheral blood smears showed rare large blastic cells. A bone marrow biopsy demonstrated a markedly hypercellular bone marrow virtually entirely replaced by blastic cells. Flow cytometric immunophenotyping revealed a large population of cells in the "blast region" that were dim CD45, dim CD117, CD34, CD33, CD7, and TdT. These cells lacked expression of lineage-specific markers for T, B, myeloid, or monocytic cells. The findings raised the possibility of an AML with minimal differentiation. However, the diffuse lymphadenopathy was unusual for AML. A concurrent lymph node biopsy showed diffuse proliferation of large cells with morphologic and immunophenotypic features similar to those present in the bone marrow. Additional flow cytometric and immunohistochemical studies revealed that the neoplastic cells were strongly positive for CD123 and CD56. The morphologic findings and the unique immunophenotype of the neoplastic cells were consistent with BPDCN. The patient was treated with chemotherapy using AML protocols followed by hematopoietic stem cell transplant, and she has been in remission for 4 months. We use this case to illustrate and review the diagnostic features of BPDCN.