The diagnosis of Sezary syndrome on peripheral blood by flow cytometry requires the use of multiple markers

Background Diagnosis of Sezary syndrome (SS)-defining blood involvement is hampered by the lack of Sezary cell-specific markers and nonspecific morphology of the tumour cells. Objectives To identify the most reliable and easy to use markers for the diagnosis of SS-defining blood involvement. Methods We studied 17 patients with SS and 11 control patients. We used flow cytometry for the detection of T-cell antigens (CD3, CD4, CD7 and CD8), expression of the Sezary cell-associated marker CD158k and T-cell receptor (TCR)-V beta chain. Additionally, Sezary cells were identified by peripheral blood smear for lymphocytes with cerebriform nuclei. Results It was not possible to diagnose blood involvement in all patients with SS by a single marker or method, although none of the markers was increased in the control population. Sezary cells were detected by blood smears in 13 of 17 (76%), by flow cytometry by their CD4+ CD7- CD3(dim) phenotype (> 1000 cells mu L(-1)) in 13 of 17 (76%) and by expression of CD158k in 11 of 17 (65%) patients with SS. A specific T-cell clone was identified by identical TCR-V beta chain expression in 12 of 17 (71%) patients with SS. The identification of Sezary cells in individual patients varied for the different markers investigated. Conclusions The combination of identifying CD4+ CD7- CD3(dim) cells, TCR-V beta chain and CD158k expression allowed a definite identification of SS-defining blood involvement in every individual patient. All of these markers can be measured by flow cytometry which would avoid time-consuming analysis of blood smears. These markers would also be suitable to monitor tumour cell load during therapy.