Sézary syndrome and Mycosis fungoides are diseases in which lymphocytes (a type of white blood cell) become malignant (cancerous) and affect the skin. In Sézary syndrome, cancerous T-cells are found in the blood. Also, skin all over the body is reddened, itchy, peeling, and painful. There may also be patches, plaques, or tumors on the skin. It is not known if Sézary syndrome is an advanced form of mycosis fungoides or a separate disease. See Mycosis Fungoides for signs, symptoms and treatments.