The Challenge of Diagnosing Acute Myeloid Leukemia or Blastic Plasmacytoid Dendritic Cell Neoplasm: A Case Report.

Background/aim: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and highly aggressive hematologic cancer which is difficult to diagnose and has a lot of overlapping features with other diseases, particularly acute myeloid leukemia (AML). BPDCN shares several immunophenotypic markers with AML, such as CD4, CD56, CD123, and HLA-DR, stating the importance of having extending panel of specific immunohistochemical (IHC) markers.

Case report: This report details a case of CLL who presented with worsening symptoms of recurrent infections and leukocytosis. A bone marrow biopsy showed immunoprofile of the blast-like population with CD4-, CD56-, and CD123- positive and CD34- and CD117- negative, based on which BPDCN was diagnosed and patient was started on first-line therapy for BPDCN. However, an extended panel of IHC stains showed positivity for lysozyme, and negativity for TCL1, MPO, and CD303. Thus, BPDCN was excluded according to the WHO 5th edition criteria, and a diagnosis of AML with monocytic differentiation was confirmed.

Conclusion: AML with monocytic differentiation can express CD4, CD56, and CD123, which are very often the only markers considered for diagnosis of BPDCN. An extended panel of IHC analysis is required before making a definitive diagnosis of BPDCN.