The different subtypes of ATLL, as per the Shimoyama classification, are consistently described as distinct entities based on their clinical features, outcomes, and even molecular profiles. Nevertheless, the aggressive subtypes - acute and lymphoma – are often analyzed together, which can obscure the unique clinical and biological characteristics of each, thereby complicating efforts to fully understand this complex and difficult-to-treat disease.

The aim of this study is to describe a cohort of patients with the lymphomatous type of ATLL in Latin America.

We conducted a cohort study involving patients aged ≥18 years with newly diagnosed ATLL, selecting all cases of the lymphoma subtype from the T-cell Brazil Project (TCBP, ambispective; ClinicalTrials.gov ID: NCT03207789, 2015–2025; n = 51) and the Grupo de Estudio Latinoamericano de Linfoproliferativos (GELL, retrospective; 2000–2023; n = 126). Clinical and biological data at diagnosis were collected, along with information on treatment, response, and follow-up. Survival was estimated using the Kaplan–Meier method, and comparisons between survival curves were made using the log-rank test. Cox regression models were applied to identify prognostic factors for overall survival (OS) and event-free survival (EFS), with a significance level set at 5%.

This analysis included a total of 177 cases: 100 from Peru, 51 from Brazil, 13 from Chile, 7 from Argentina, and 6 from Colombia. The median age was 54 years (20–95), with 50% male, 83% had advanced-stage disease (Ann Arbor stage III–IV), 44% extranodal involvement, 61% having an IPI score of 3–5, and 59% having a PIT score of 2–4. Treatment intent was considered potentially curative in nearly 97% (72% chemotherapy (CT) alone, 18% CT + AZT and IFN, 7% AZT + IFN). CHOP-like was the most used, (43% CHOP and 29% CHOEP). After first-line therapy, 28% had a complete response (CR), while 39% no response/progressive (PD). Only 5 patients (3%) underwent hematopoietic cell transplantation (HCT) as consolidation after first-line therapy. Myeloablative allogeneic HCT was performed in two patients in complete remission (CR): one relapsed and died, while the other remains in CR. Two patients received non-myeloablative allogeneic HCT; one experienced disease progression post-HCT and was subsequently treated with a donor lymphocyte infusion, and both are currently in CR. One patient received an autologous HCT, achieving partial remission (PR). In general, 68% had progression/relapse. The median follow-up duration of the survivors was 14 months (1-182). 24-month OS was 28% and 18% for EFS. The final Cox model for OS was median age ≥ 54y (HR 2.35 95%CI 1.55-3.57, p < 0.0001), ECOG ≥2 (HR 1.90 95%CI 1.22-2.97, p = 0.005), higher LDH (HR 2.77, 95%CI 1.50-5.10, p = 0-.001) and B symptoms (HR 2.65, 95%CI 1.61-4.37, p < 0.0001), and for EFS the final model was compound with the same prognosis factors.

To our knowledge, this study represents the largest cohort of the ATLL lymphoma subtype in Latin America and suggests that OS and EFS for this malignancy remains poor, primarily due to advanced stage at diagnosis, high-risk clinical features, and limited access to adequate therapy. These findings underscore the need for a richer understanding of the condition to enable appropriate risk stratification.