Adult T-cell leukemia/lymphoma (ATL or ATLL) is a rare cancer of the immune system's T-cells caused by human T cell leukemia/lymphotropic virus type 1 (HTLV-1). All ATL cells contain integrated HTLV-1 provirus further supporting that causal role of the virus in the cause of the neoplasm. A small amount of HTLV-1 individuals progress to develop ATL with a long latency period between infection and ATL development.  ATL is categorized into 4 subtypes: acute, smoldering, lymphoma-type, chronic. Acute and Lymphoma-type are known to particularity be aggressive with poorer prognosis.

Globally, the retrovirus HTLV-1 is estimated to infect 20 million people with the incidence of ATL approximately 0.05 per 100,000 with endemic regions such as regions of Japan, as high as 27 per 100,000. However, cases have increased in non-endemic regions with highest incidence of HTLV-1 in southern/northern islands of Japan, Caribbean, Central and South America, intertropical Africa, Romania, northern Iran. ATL normally occurs around the age of 62 years but median age at diagnosis does depend on prevalence of the HTLV-1 infection in the geographic location.

Current treatment regiments for ATL are based on clinical subtype and response to initial therapy. Some therapy modalities for treatment may not available in all countries therefore strategies differ across the world. All patients are referred to clinical trials if available. Beyond clinical trials, treatments are centered on multiagent chemotherapy, zidovudine plus interferon a (AZT/IFN), and allogenic hematopoietic stem cell transplantation (alloHSCT).