Adult T-cell leukemia is a type of cancer that affects the immune system. It is caused by a virus called human T-cell lymphotropic virus type 1 (HTLV-1) and is characterized by abnormal growth of T-cells in the body. Some common synonyms for adult T-cell leukemia are HTLV-1-associated lymphoma/leukemia, adult T-cell lymphoma, and adult T-cell leukemia/lymphoma. Although the disease is relatively rare, it can be fatal if not treated promptly. Symptoms of adult T-cell leukemia include skin lesions, fever, night sweats, and weight loss. Treatment options include chemotherapy, radiation therapy, and bone marrow transplantation, depending on the severity of the disease.