[Development of future treatment for ATL]

Adult T-cell leukemia/lymphoma (ATL) is a peripheral T-cell malignancy caused by human T-cell leukemia virus type I. The clinical course of ATL is heterogeneous, and this condition has different types, which are as follows: acute, lymphoma, chronic, and smoldering. The chronic type is further subclassified into favorable and unfavorable subtypes. Acute, lymphoma, and unfavorable chronic type ATL and favorable chronic and smoldering-type ATL are defined as aggressive and indolent ATL, respectively. Newly identified prognostic indices based on clinical parameters and/or genetic predictors should be incorporated in the stratified treatment approach. The standard of care for aggressive ATL is multiagent chemotherapy, followed by allogeneic hematopoietic stem cell transplantation if applicable. Meanwhile, that for indolent ATL is watchful waiting until progression to the aggressive type. The combination of interferon-α and zidovudine is a treatment option for indolent ATL in other countries, and a confirmatory phase 3 trial is ongoing in Japan. In addition to mogamulizumab, lenalidomide, and brentuximab vedotin, which have been recently utilized in clinical practice, the use of a novel histone deacetylase (HDAC) inhibitor has been filed for approval. Moreover, an EZH1/2 inhibitor has completed the enrollment of a phase 2 trial in Japan. The standard of care for elderly patients should be established because the median age of those with newly diagnosed ATL reaches up to 70 years old.