Prospective validation of podoplanin expression as a diagnostic biomarker of acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a medical emergency that needs immediate diagnosis and treatment. Podoplanin, a transmembrane glycoprotein that binds CLEC-2 on platelets, was recently demonstrated to be abnormally expressed in leukemic blasts in APL, as opposed to other forms of AML, in a study using thawed primary cells. This study aimed to explore and validate the diagnostic accuracy of measuring podoplanin expression by flow cytometry in the differential diagnosis of APL and other forms of acute myeloid leukemia (AML) as part of the diagnostic work-up of all cases suspected of AML in an academic hematology center. Podoplanin expression was measured by flow cytometry in bone marrow samples obtained at disease presentation from all consecutive adult patients suspected of AML. Results from 24 APL patients were compared with those from 23 non-APL AML patients matched by age and sex. Markedly higher PDPN expression was observed in APL patients when compared to other AML patients, with an area under the curve of 0.92 (95%CI: 0.82-1.0, p < 0.0001) for the percentage of positive cells. Combining an optimal cutoff of 7.66% for PDPN-positive blasts and 1691 for the mean fluorescence index of PDPN expression, APL was identified with a sensitivity of 87.5% and a specificity of 100%. Moreover, PDPN expression presented a negative correlation with platelet count and fibrinogen levels. PDPN expression measured by flow cytometry can accurately differentiate between APL and other forms of AML in a real-world clinical setting, contributing to the diagnosis of this form of acute leukemia. If confirmed in larger prospective studies, the negative association of PDPN expression with fibrinogen and platelet counts supports the concept that this biomarker can potentially contribute to the clinical characterization of APL.