While some groups have previously advocated for a simplified flow cytometry approach based on the quantification of CD4+ T cells lacking CD7 and/or CD26 expression (most common Sezary cell immunophenotype) [65,68], others have found this approach to be suboptimal, as these immunophenotypic features are not specific for neoplasia and consistently include benign T-cell subsets, which are commonly expanded in reactive conditions [69,70,71]. This evidence concerns the gene CD7 and neoplasm.