A 74-year-old man was diagnosed as having Sézary syndrome in 1999. Treatment with combination chemotherapy could not completely control both the erythroderma and Sézary cells. However, treatment with oral administration of etoposide was able to maintain the patient in a good condition for about 4 years. In June 2004, he developed topoisomerase II inhibitor-related acute promyelocytic leukemia. Chromosomal analysis demonstrated abnormalities of t(1;10) (q21;q26) and t(15;17) (q22;q12) in 17 of 20 cells. Despite treatment with ATRA and combination chemotherapy, the patient died of brain hemorrhage.