AbstractAimLittle is known about the outcome and prognostic factors of relapsed or refractory T‐cell lymphoblastic lymphoma (T‐LBL), especially in adult patients. The aim of this study was to analyze the characteristics, outcome and prognostic factors for this patient population.MethodsBetween January 2006 and December 2017, we retrospectively analyzed 84 adult patients with T‐LBL, and 44 relapsed or primary refractory patients were included in this analysis. Clinical features, treatment and follow‐up information were collected.ResultsFor all 44 patients, the median time to disease progression or relapse was 9.5 months after diagnosis. At a median follow‐up of 19.6 months, 40 (90.9%) patients died. The 3‐ and 5‐year overall survival (OS) rates after disease progression or relapse were 7.8% and 5.2%, respectively. Among 30 patients who had detailed information of second‐line treatment, only eight achieved a second complete remission (CR). Two of these eight patients subsequently underwent autologous or allogeneic stem cell transplantation (SCT), of whom one died from disease progression after autologous SCT, and one was free of event at 84 months after allogeneic SCT. Three of the rest six patients in second CR were still alive after chemotherapy alone. All the remaining patients who failed to gain second CR eventually died. In univariate analysis, only the achievement of second CR was positively predictive of OS (hazard ratio (HR) = 0.307; 95% confidence interval (CI), 0.104–0.905; P = 0.032).ConclusionThe outcome of adult patients with relapsed or refractory T‐LBL is extremely dismal. Patients with relapsed or refractory T‐LBL should be encouraged to participate in clinical trials where novel therapeutic approaches are available.