Distribution of adult T‐cell leukaemia/lymphoma subtypes and survival outcomes across geographical regions: An international retrospective cohort study

Summary Although adult T‐cell leukaemia/lymphoma (ATL) has a higher burden in certain world regions, outcomes have not been directly compared across regions. We conducted a multicentre cohort study comparing the distribution of ATL subtypes and overall survival (OS) across 1090 adults (≥18 years) diagnosed with ATL during 2000–2023 in Japan ( n = 366), South America ( n = 364), the United States ( n = 275) and the United Kingdom ( n = 85). Survival was estimated using Kaplan–Meier methods. Acute ATL was more frequent in Japan (59%) than in the United States (45%), South America (36%) and the United Kingdom (24%) ( p heterogeneity < 0.0001). Conversely, lymphomatous ATL predominated in the United Kingdom (53%), South America (51%) and the United States (45%) relative to Japan (20%) ( p heterogeneity < 0.0001). With a median follow‐up of 38 months interquartile range (IQR 14–68), 3‐year OS across regions ranged from 10% to 25% for acute, 16%–34% for lymphomatous, 49%–86% for chronic and 60%–83% for smouldering ATL. Evidence of regional differences in OS was observed for acute, lymphomatous and chronic ATL but not for smouldering ATL. In conclusion, the distribution of ATL subtypes varies globally, and OS for aggressive subtypes (i.e. acute and aggressive) remains poor across regions. Our findings could guide the design of clinical studies aimed at developing accessible therapies through international collaboration.