Outcomes of patients with HTLV-1 adult T-cell leukemia/lymphoma (ATLL) after allogeneic SCT: results of the EBMT LWP.

Adult T-cell leukemia/lymphoma (ATLL) is a rare HTLV-1-associated malignancy with a dismal prognosis due to intrinsic chemoresistance and immunosuppression. This retrospective EBMT registry analysis evaluated outcomes of allogeneic stem cell transplantation (allo-SCT) in 73 ATLL patients transplanted between 2004 and 2021. With a median follow-up of 3.9 years, 2-year overall survival (OS) and progression-free survival (PFS) were 49% (95% CI 37-60) and 43% (95% CI 31-54), respectively. Non-relapse mortality was 7% at 2 years, while relapse incidence (RI) was 49.8%. Multivariate analysis identified haploidentical donors as associated with improved OS, while non-CR status at transplant was independently associated with significantly worse PFS (HR 2.93, p = 0.01), OS (HR 4.12, p = 0.002), and RI (HR 2.66, p = 0.04) compared to CR. Our findings suggest that allo-SCT represents a feasible and potentially curative consolidation strategy for ATLL patients, with CR at transplant, younger age, and haploidentical donors being independent predictors of improved survival, supporting the importance of disease control, patient selection, and alternative donor strategies.