For the diagnosis of SS, the International Society for Cutaneous Lymphomas (ISCL) propose that the presence of a monoclonal population in the skin and blood (same clone) and one of the phenotypic alterations (CD4/CD8 ≥ 10 and/or CD4+CD7- ≥ 40% and/or CD4+CD26- ≥ 30%) or detection of more than 1,000 Sézary cells/μL are mandatory (Table 1) (3, 10, 73). Here, DPP4 is linked to synovial sarcoma.