Peripheral blood Sézary cells and the diagnosis of Sézary syndrome

Sézary syndrome (SS) is a rare and aggressive cutaneous lymphoma, and its diagnosis is based both on clinical, histological and biological features. None of these criteria taken alone is specific, and the two clinical observations reported here agree with this. Peripheral blood involvement, due to the presence of a variable number of Sézary cells, has been recently fully delineated by the ISCL/EORTC international organizations, and taken into account in the diagnosis and the prognosis of this syndrome. Identification and quantification of peripheral blood Sézary cells on the blood smear is an essential criterion for the diagnosis and is sufficient when associated with relevant clinical or/and histological grounds. Flow cytometry is another tool to demonstrate Sézary cells within the peripheral blood mononuclear cells. The authors discuss about the respective advantages and limits of morphology and flow cytometry in the identification and enumeration of circulating Sézary cells. Molecular biology is helpful in peculiar situations.