Allogeneic Hematopoietic Cell Transplantation for Relapsed or Refractory Mantle Cell Lymphoma: Real‐World Outcomes, Late Relapse Patterns, and Clinical Utility in the Chimeric Antigen Receptor T‐Cell Era

ABSTRACT Background Allogeneic hematopoietic cell transplantation (alloHCT) remains a curative option for relapsed or refractory (r/r) mantle cell lymphoma (MCL), although its role has shifted in the era of Bruton tyrosine kinase inhibition (BTKi) and chimeric antigen receptor T‐cell (CAR‐T) therapy. Real‐world evidence on long‐term outcomes and salvage strategies after relapse is limited. Methods We performed a retrospective analysis of 29 patients with r/r MCL who underwent alloHCT between 2001 and 2017 using either higher‐intensity or reduced‐intensity conditioning. Outcomes assessed included overall survival (OS), progression‐free survival (PFS), relapse incidence, and non‐relapse mortality (NRM), focusing on relapse timing and management. Conditioning regimens were compared exploratorily. Results With a median follow‐up of 143 months (95% CI: 104–NR), 3‐year OS and PFS were 41% and 34%, respectively. Relapse occurred in 38% of patients, including over one quarter with late (> 12‐month), predominantly localized relapse. Salvage radiotherapy, alone or combined with BTKi, achieved durable disease control in about two‐thirds of patients. Differences between higher‐intensity and reduced‐intensity conditioning were observed but remained exploratory and not statistically conclusive. Conclusion In this real‐world cohort, alloHCT provided sustained disease control for a subset of r/r MCL patients, including late, localized relapse amenable to salvage therapy. As alloHCT is now performed less frequently, such datasets are critical for decision‐making in patients after CAR‐T ineligibility or failure, especially where CAR‐T access is limited. These findings support a continued, selective role for alloHCT in the modern treatment landscape and emphasize the need for real‐world evidence to guide patient selection and sequencing in the CAR‐T era. Trial Registration The authors have confirmed clinical trial registration is not needed for this submission.