Sézary syndrome (SS) is a rare and aggressive type of cutaneous T-cell lymphoma (CTCL) characterized by an intense pruritus, erythroderma (>80% involvement of the body surface), and the systemic dissemination of clonal CD4+ T cells into the blood and, often, the lymph nodes. The gene discussed is CD4; the disease is primary cutaneous T-cell non-Hodgkin lymphoma.