Gain of CD26 expression on the malignant T-cells in relapsed erythrodermic leukemic mycosis fungoides

Abstract

Loss of CD26 surface expression on the circulating malignant T-cell is the most widely accepted diagnostic marker in patients with leukemic cutaneous T-cell lymphoma (CTCL). CTCL cases with reemergence of CD7 and/or CD26 surface expression are unusual and of uncertain prognosis. We report the case of an erythrodermic leukemic mycosis fungoides patient who had achieved temporary remission after a several months on multimodality immunotherapy and extracorporeal photopheresis, but who relapsed with aggressive disease phenotypically characterized by CD4+ T-cells with high CD26 expression. Polymerase chain reaction (PCR) studies and high throughput sequencing analyses from peripheral blood mononuclear cells at presentation and relapse consistently showed an identical clonal T-cell receptor (TCR) suggesting evolution of her original malignant clone which lacked CD26 expression. Interestingly, quantitative expression of the sialomucin, CD164, mirrored her clinical picture, thus favoring its reliability as a novel biomarker in CTCL.

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