P1273: comparison of total body irradiation-based with chemotherapy-based myeloablative conditioning regimens in patients with b-cell acute lymphoblastic leukemia in first complete remission

Topic: 22. Stem cell transplantation - Clinical Background: Acute lymphoblastic leukemia (ALL) is one of the most common acute leukemia in adults, accounting for about 20%~30% of adult acute leukemia. Hematopoietic stem cell transplantation (HSCT) has become a standard of care for patients with ALL. Total body irradiation (TBI)-based conditioning regimens constituted the central part of conditioning regimen for HSCT but were also associated with acute and long-term toxicity, increased treatment-related mortality and increased risk of secondary malignancy. Few studies comparing chemotherapy-based with TBI-based conditioning regimens suggested similar survival but a higher relapse rate in chemotherapy-based conditioning regimens. Thus, the ideal conditioning regimen for HSCT in ALL remains controversial Aims: To compare the efficacy of chemotherapy-based and TBI-based conditioning regimens in patients with B cell-acute lymphoblastic leukemia (B-ALL) in first complete remission (CR1) and provide the theoretical basis for clinical decision-making in the futu Methods: We retrospectively investigated the outcomes of 177 adult patients with B-ALL in CR1 in our center from Jan 2019 to Dec 2021. The overall survival (OS), leukemia-free survival (LFS), cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) rate and the impact of minimal residual disease (MRD) after 3 chemotherapy cycles along with donor type in conditioning regimen selection were explored. Results: Between Jan 2019 and Dec 2021, 177 patients were included, of which 61 received chemotherapy-based conditioning and 116 received TBI. We divided patients into 3 groups according to donor type and MRD status after 3 chemotherapy cycles. For autologous hematopoietic stem cell transplantation (auto-HSCT) patients with negative MRD after 3 chemotherapy cycles, the 2-year OS (93.3% vs 100.0%, P=0.317), LFS (72.3% vs 80.0%, P=0.628), CIR (27.7% vs 20.0%, P=0.628) and NRM rates (0% vs 0%, P=1.0) were similar between TBI and chemotherapy-based regimens. In allogeneic hematopoietic stem cell transplantation (allo-HSCT) patients with negative MRD, there was a lower trend of 2-year OS (62.5% vs 89.2%, P=0.058) as a result of higher NRM (40.2% vs 5.2%, P=0.023) in TBI-based regimens while LFS (52.9% vs 70.7%, P=0.227) and CIR rates (6.9% vs 24.0%, P=0.293) were not significantly different. As for other allo-HSCT patients with positive MRD after 3 chemotherapy cycles, TBI-based regimens showed evidence of benefit compared with chemotherapy-based conditioning regimens in terms of LFS (70.7% vs 39.4%, P=0.042) and relapse rates (18.4% vs 52.6%, P=0.019). Summary/Conclusion: Chemotherapy-based pretreatment schemes appears to be an attractive treatment option for patients with B-ALL in CR1 especially for those who achieved negative MRD after 3 chemotherapy cycles. For MRD positive patients, TBI-based pretreatment schemes may be more effective from relapse.Keywords: Hematopoietic cell transplantation, Total body irradiation, Minimal residual disease (MRD), ALL