Post Transplant Cyclophosphamide Following Myeloablative TBI As a Conditioning Regimen for High-Risk Patients with AML Who Relapse after Transplant with Busulfan-Containing Regimen

Introduction Allogeneic HSCT (alloHSCT) offers a potential cure for patients with AML; however, 40% of AML patients receiving alloHSCT will experience relapsed disease. Second alloHSCT can offer the best long-term survival but is associated with significant toxicity. Preliminary data suggests that TBI only preparative regimen with post-transplant HD Cy is associated with lower TRM compared to TBI/Cy. Methods We report on four patients with AML who experienced relapsed disease following alloHSCT with busulfan-containing preparative regimen. All patients received re-induction chemotherapy and 3 achieved remission. Two patients had significant pre-existing morbidities prior to transplant, and one patient had refractory disease. Each patient received a second alloHSCT transplant using a TBI only preparative regimen (1200-1320 cGy) and GVHD prophylaxis included HD Cy 50mg/kg/daily on Days +3 and +4 as well as tacrolimus and MMF starting on Day +5. MMF was discontinued at Day +30 post-transplant. Three patients received bone marrow from 10/10 HLA-matched unrelated donors. One patient received PBSC from an HLA matched parent donor. Results All four patients tolerated transplant with no transplant related mortality and no grade 3 toxicity. All patients achieved neutrophil and platelet engraftment at an average of 19.5 (range 14-25) and 19 (range 15-23) days post transplant, respectively. Fifty percent of the patients developed acute Grade I-II skin GVHD. One patient developed mild, limited chronic GVHD. All patients are currently alive and are at least one year post second-transplant. Three of the four (75%) patients are off immune suppression and remain in remission at 14, 15 and 20 months post HSCT. Conclusion TBI only preparative regimen with post transplant HD Cy may offer an alternative treatment option for AML patients who experience relapse following a prior busulfan-containing alloHSCT.