[Adult T-Cell Leukemia/Lymphoma (ATL)].

Adult T-cell leukemia/lymphoma (ATL) is a distinct malignancy of CD3+/CD4+/CD8-/CD25+/CCR4+/FoxP3+ or -/TdT- Treg/Th2 cells that is etiologically associated with human T-cell lymphotropic virus type I (HTLV-1), which is endemic in several regions in the world including southwest Japan. ATL is a rare malignancy and is a single HTLV-1-mediated disease entity with diverse molecular features. Additionally, ATL clinical features and prognosis are diverse, leading to subtype classification into acute, lymphomatous, chronic, and smoldering types according to organ involvement and LDH and calcium levels. For the acute, lymphomatous, or unfavorable chronic subtypes (aggressive ATL) and favorable chronic or smoldering ATL (indolent ATL), intensive chemotherapy followed by allo-HSCT and careful observation until disease progression has been recommended in Japan, respectively. Maintenance of a medical treatment system for ATL, a rare leukemic lymphoma with diverse clinical features and poor prognosis, is required in Japan and other endemic areas in the world.