Nevertheless, numerous studies analyzed CD26/DPP4 cell surface expression and levels of sCD26/DPP4 in the serum of patients with cutaneous T-cell lymphoma (CTCL) including the most frequent CTCL mycosis fungoides (MF) and Sézary syndrome (SS) [120]. Here, DPP4 is linked to primary cutaneous T-cell non-Hodgkin lymphoma.