Abstract
BACKGROUND: Mycosis fungoides (MF) and Sézary Syndrome (SS) are clinically distinct cutaneous T-cell lymphomas with strikingly similar morphologic and phenotypic features. Prior studies have suggested phenotypic differences based on markers of antigen experience, suggesting a different cell of origin. METHODS: Seventy-nine involved peripheral blood or bone marrow samples from 33 patients with SS and 19 patients with MF were studied by 10-color flow cytometry, including CD62L, CD45RA, CCR4, and PD-1. Gated tumor events were classified as naïve (T(N) ), central memory (T(CM) ), effector memory (T(EM) ), or effector memory with reacquired CD45RA (T(EMRA) ); based on CD62L(+) /CD45RA(+) , CD62L(+) /CD45RA(-) , CD62L(-) /CD45RA(-) , or CD62L(-) /CD45RA(+) phenotype, respectively. Sequential specimens were compared to assess for phenotypic stability. RESULTS: The naïve/memory phenotype of the neoplastic T-cells was markedly heterogeneous, with a dominant T(N) , T(CM) , T(EM) , or T(EMRA) subset on 11 (14%), 32 (41%), 30 (38%), and 6 (8%) cases, respectively. There was no correlation between the diagnosis of MF or SS and putative cell of origin (P = 0.4). Overexpression of CCR4 and PD1 was observed in most cases, with higher intensity in SS compared to MF. The naïve/memory phenotype remained the same for 10 patients up to 273 days after the initial analysis; while on six patients, the naïve/memory phenotype was different from the original phenotype. CONCLUSIONS: Both SS and MF can have phenotypic features of any of the major naïve/memory T-cell subsets, which questions the current principle of "cell-of-origin" distinction between SS and MF. Phenotypic shifts within these subsets are common, suggesting a functional state rather than a cell-of-origin surrogate. © 2018 International Clinical Cytometry Society.