Hematologic involvement is stratified into B0 (no blood involvement, ≤ 5% Sézary cells or < 250/μL of CD4+CD26- or CD4+CD7- cells), B1 (low blood tumor burden, with > 5% Sézary cells or ≥ 250/μL of CD4+CD26- or CD4+CD7- cells, but not meeting the criteria for B2), and B2 (high tumor burden in the blood, with ≥ 1,000 Sézary cells/μL, an increase in CD4+ cells with a CD4/CD8 ratio ≥ 10, CD4+/CD7- ≥ 40%, CD4+/CD26- ≥ 30%, ≥ 1000/μL of CD4+CD26- or CD4+CD7- cells, or other aberrant population of lymphocytes identified by flow cytometry). The gene discussed is DPP4; the disease is neoplasm.