Impact of total body irradiation‐ vs chemotherapy‐based myeloablative conditioning on outcomes of haploidentical hematopoietic cell transplantation for acute myelogenous leukemia

The optimal myeloablative conditioning (MAC) for patients undergoing haploidentical hematopoietic cell transplantation (haplo‐HCT) is unknown. We studied the outcomes of total body irradiation (TBI) vs chemotherapy (CT) based MAC regimens in acute myeloid leukemia (AML) patients. The study included 1008 patients who underwent first haplo‐HCT with post‐transplant cyclophosphamide, following TBI (N = 89, 9%) or CT (n = 919, 91%) based MAC. Patients in the TBI cohort were younger (median age, 38 vs 47 years, P < .01) and more likely to receive BM graft (57% vs 43%, P = .01). Two‐year overall chronic GVHD (cGVHD) incidence was 42% vs 27% ( P < .01) and extensive cGVHD incidence was 9% vs 12% ( P = .33) in TBI and CT cohorts, respectively. Graft failure was reported in two (2%) TBI‐ and 65 (7%) CT‐MAC recipients ( P = .08). Death from veno‐occlusive disease was reported in one (3%) TBI and 11 (3%) CT patients who died during the study period. In the multivariate analysis, TBI was associated with increased risk for overall cGVHD (hazard ratio = 1.95, 95% confidence interval:1.2‐3.1, P < .01) compared to CT‐based MAC. The choice of conditioning regimen did not impact relapse incidence, leukemia‐free survival, non‐relapse mortality, overall survival or GVHD‐relapse‐free survival in multivariate analysis. In conclusion, major transplant outcomes were not statistically different between TBI‐based MAC and CT‐based MAC in patients with AML after haplo‐HCT/PTCy.