Higher total body irradiation dose-intensity in fludarabine/TBI-based reduced-intensity conditioning regimen is associated with inferior survival in non-Hodgkin lymphoma patients undergoing allogeneic transplantation: Flu/2Gy TBI vs Flu/4Gy TBI in NHL
INTRODUCTION Disease relapse is the most common cause of therapy failure in non-Hodgkin lymphoma (NHL) patients undergoing reduced-intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (alloHCT). It is not known whether or not increasing total body irradiation (TBI) dose from 2Gy to 4Gy in RIC-platform can provide improved disease control without increasing non-relapse mortality (NRM). Using the CIBMTR database we evaluated
the outcomes of NHL patients receiving RIC alloHCT with either fludarabine (Flu)/2Gy TBI vs. Flu/4Gy TBI. METHODS In the CIBMTR registry, 413 adult NHL patients underwent a first alloHCT using either a matched related or unrelated donor between 2008-2017, utilizing a RIC regimen with either Flu/2Gy TBI (n=349) or Flu/4Gy TBI (n=64). The primary endpoint was overall survival (OS). Secondary endpoints included acute (a) and chronic (c) graft-versus-host disease (GVHD), NRM, relapse/progression and progression-free survival (PFS). RESULTS At baseline the Flu/2Gy TBI cohort had significantly fewer patients with KPS ≥90 and significantly more patients had a higher HCT-CI. On multivariate analysis the two conditioning cohorts were not significantly different in terms of risk of grade 3-4 aGVHD or cGVHD. Compared to Flu/2Gy TBI, the Flu/4Gy TBI conditioning was associated with a significantly higher risk of NRM (HR 1.79, 95%CI=1.11-2.89, p=0.02), and inferior OS (HR 1.51, 95%CI=1.03-2.23, p=0.03). No significant differences were seen in the risk of relapse/progression (HR 0.78, 95%CI=0.47-1.29, p=0.33) or PFS (HR 1.09, 95%CI=0.78-1.54, p=0.61) between the two regimens. Comparing Flu/2Gy TBI vs. Flu/4Gy TBI cohorts the 5-year adjusted outcomes were; NRM (28% vs. 47%; p=0.005), relapse/progression (35% vs. 29%; p=0.28), PFS (37% vs. 24%; p=0.03) and OS (51% vs. 31%; p=0.001), respectively. Relapse was the most common cause of death in both cohorts. CONCLUSIONS In NHL patients undergoing Flu/TBI-based conditioning, augmenting TBI dose from 2Gy to 4Gy is associated with higher NRM and inferior OS, without any significant benefit in terms of disease control. 2Gy is optimal dose in the RIC Flu/TBI platform for lymphomas.