Podoplanin Expression Measured By Flow Cytometry Accurately Identifies Patients with Acute Promyelocytic Leukemia at Diagnosis

Acute promyelocytic leukemia (APL) is a hematological emergency associated with high early mortality rates, thus requiring prompt diagnosis and treatment initiation. Currently, diagnostic suspicion relies on morphological criteria, which can be further corroborated by immunophenotypic analyses, until results based on molecular techniques confirm the diagnosis. However, while both cytology and immunophenotypic analyses are very important in this setting, their accuracy can be influenced by inherent morphological variation of blasts, as well as by gating and other technical issues related to flow cytometry. In this context, novel parameters that could contribute to the segregation of APL from other forms of acute myeloid leukemia (AML) would be desirable. Recently, Lavallée et al demonstrated that the aberrant expression of podoplanin (PDPN), a protein that mediates platelet activation in inflammatory contexts, by leukemic cells is as a relevant mediator of the coagulopathy of APL, as well potential biomarker of this condition based on the analysis of primary cells from patients with AML. The aim of this study was to prospectively and independently validate whether the surface expression of PDPN by leukemic promyelocytes measured by flow cytometry can contribute to the differential diagnosis between APL and other forms of AML. We also explored the association of PDPN expression with clinical and laboratory characteristics of these patients. The study population consisted of all consecutive patients diagnosed with APL by cytological, immunophenotypical and molecular techniques in our adult academic hematology hospital from 2020 to 2023. Exclusion criteria included the presence of hemodynamic instability or refusal to participate. The expression of PDPN was measured by flow cytometry using BD FACSCanto II™ cytometer. Analysis was performed in accordance with EuroFlow protocols, with a panel that includes CD45, CD33, CD34, MPO, CD117, CD13, HLA-DR, as well as an antibody against PDPN (PE anti-human Podoplanin Antibody - Catalog# 337004 - BioLegend). Lymphocytes were used as internal negative control for PDPN expression. Data were analyzed with Infinicyt™ software and reported both as the % of PDPN + cells or according to mean fluorescence intensity (MFI). Patients with other forms of AML diagnosed during the same period and matched for age, gender and peripheral blast count were used to compare the diagnostic accuracy of PDPN measurement. Clinical and laborator