Blood flow cytometry in Sézary syndrome: new insights on prognostic relevance and immunophenotypic changes during follow-up.

OBJECTIVES Sézary syndrome (SS) is characterized by erythroderma, generalized lymphadenopathy, and the presence of circulating atypical lymphocytes, which are difficult to identify by morphologic data. METHODS We revised our series of 107 patients in an attempt to better define the phenotypic aberrancies in blood at diagnosis and the immunophenotypic stability over time detected by flow cytometry. Polymerase chain reaction assay was also used to study CD26/dipeptidyl peptidase IV (DPPIV) gene methylation. RESULTS The most common aberrancies were represented by the lack of CD26 (96/107) or CD38 (101/107) expression and the presence of a "dim" CD3, CD4, or CD2 population. There was a high variability in CD7 expression. In total, 31% of the patients had phenotypical heterogeneity in CD26 and CD7 expression at diagnosis. The phenotype was stable over time in 73 of 95 patients with available follow-up data, while 22 of 95 patients developed changes in CD26, CD7, or CD2 expression. CD4+CD26- SS showed hypermethylation of the CpG islands for the promoter region of CD26/DPPIV. Multivariate analysis showed that CD26 expression is a favorable prognostic factor (hazard ratio, 2.94; P = .045). CONCLUSIONS We confirm the relevance of CD26 negativity in SS diagnosis and monitoring. Nevertheless, the presence of rare CD26+ cases suggests that a multiparameter flow cytometry approach should be used. Changes in methylation profile could account for phenotypical heterogeneity.