Revisiting the initial diagnosis and blood staging of mycosis fungoides and Sezary syndrome with the KIR3DL2 marker

Background The early diagnosis of Sezary syndrome (SS) is challenging. Loss of CD7 and CD26 expression on CD4(+) T cells is the currently used criterion in the initial diagnosis and staging of patients with SS. Objectives Our aim was to evaluate the respective value of CD26, CD7 and KIR3DL2 expression on CD4(+) T cells and total lymphocytes at initial diagnosis of SS. Methods This prospective study included 254 patients with clinical features consistent with cutaneous T-cell lymphoma seen at our institution between March 2014 and February 2019. Peripheral blood analysis by flow cytometry was performed for each patient at the time of diagnosis and during follow-up. The diagnosis of SS was based on ISCL/EORTC criteria. Results The presence of KIR3DL2(+) Sezary cells (SCs) >= 200 mu L-1 correlated with the diagnosis of SS, with sensitivity of 88 center dot 6% and specificity of 96 center dot 3%. All 154 patients with either inflammatory skin disease or other haematological disease had KIR3DL2(+) cells < 200 mu L-1, while eight of them had CD4(+) CD26(-) T cells >= 1000 mu L-1. Of five patients with SS and lymphopenia, four had CD4(+) CD7(-) T cells < 1000 mu L-1 and three had CD4(+) CD26(-) T cells < 1000 mu L-1. However, all of them had KIR3DL2(+) CD4(+) T cells >= 200 mu L-1. Among patients with available samples during evolution, all B1-staged patients with >= 200 mu L-1 KIR3DL2(+) SCs at diagnosis evolved to B2 stage within 7 months. Conclusions KIR3DL2 expression on T cells is highly specific and helps the early diagnosis of SS, especially in those patients with lymphopenia.