Event-free survival at 24 months is a robust surrogate endpoint for long-term survival in pediatric, adolescent, and adult T cell lymphoblastic lymphoma.

T cell lymphoblastic lymphoma (T-LBL) has an aggressive clinical behavior. To date, powerful and consistent prognostic factors have not been established for T-LBL. In this study, we first evaluated the association of event-free survival (EFS) at 24 months (EFS24) with overall survival (OS) in T-LBL patients. Besides, we sought to identify clinical factors of prognostic importance in this rare entity. Between January 2006 and December 2017, ninety-one patients with newly diagnosed T-LBL were retrospectively analyzed. EFS was defined as the time from diagnosis to relapse or progression, unplanned retreatment, death from any cause, or to the last follow-up. In total, 91 patients with a median age of 24 years were enrolled. At a median follow-up of 40.4 months (range, 1.4 to 163.3 months), the 5-year OS and EFS was 47.9% and 43.2%, respectively. Of all patients, 45 (49.5%) achieved EFS24 and 46 (50.5%) did not. Patients who achieved EFS24 showed a markedly superior outcome, compared with those who failed to achieve EFS24 (5-year OS, 90.5% vs 3%, P < 0.001). Univariate analysis indicated bone marrow involvement, response to induction treatment, and stem cell transplantation (SCT) consolidation to be prognostic factors for EFS and OS. In addition, compared with the patients receiving non-Hodgkin's lymphoma (NHL)-like treatment protocols, patients treated with hyper-CVAD showed significantly improved EFS and OS. Such survival advantage in terms of EFS and OS was also observed of BMF-90 regimens over NHL-like therapy, despite that the difference in EFS did not reach statistical significance (P = 0.056). Multivariate analysis demonstrated that achievement of complete remission (CR) after induction therapy and SCT consolidation were independent prognostic indicators for both EFS and OS. We confirm that EFS24 is a strong surrogate endpoint for long-term survival in T-LBL, which is clinically useful for individualized risk reassessment, future clinical trial design, and biomarker discovery validation. Further validation in the context of directed prospective clinical trials is warranted.