Ann Hematol

Patients with relapsed/refractory T-cell acute lymphoblastic leukemia (R/R T-ALL) have very poor prognosis. CAR T-cell therapy is being explored in these patients with encouraging results. Specifically, CD1a-directed CAR T-cells are being explored in clinical trials to treat cortical T-ALL (CD1a+), but there are no data on outcome in this subgroup of patients before this therapy. This retrospective, observational study aimed to describe the characteristics and outcomes of patients with R/R CD1a + T-ALL. We included pediatric and adult patients diagnosed with R/R CD1a + T-ALL in 25 sites of Spain between March 2006 and May 2022. The primary outcome of the study was overall survival (OS). Forty-three patients, 28 adults and 15 children, with R/R CD1a + T-ALL were included. Median (range) age at inclusion was 24 years (5–57), and 82.5% were male. After a median (range) follow-up of 7.0 years (5.1–13.6), 6 (14.0%) patients were alive and in complete remission (CR) and 37 (86.0%) had died. Five-year OS was 16% (95% CI; 7–29%). Bone marrow relapse, an interval < 12 months between first CR and relapse, and lack of allogeneic hematopoietic stem cell transplantation during salvage treatment were associated with worse OS. Our results confirm that patients with R/R CD1a + T-ALL have a very poor prognosis, highlighting the need for new treatment alternatives in these patients. Supplementary Information: The online version contains supplementary material available at 10.1007/s00277-026-06956-8.