DPP4 and synovial sarcoma: The diagnostic criteria for SS include the presence of a monoclonal TCR gene rearrangement on the blood and the skin, more than 1,000 Sézary cells/μL on peripheral blood, and immunophenotypic abnormalities (CD4/CD8 ≥ 10, CD4 + CD7- ≥ 40%, and CD4 + CD26- ≥ 30%)4.