Durable Engraftment with Minimal Toxicities after Allogeneic Hematopoietic Stem Cell Transplantation with a Reduced-Intensity Regimen Incorporating Fludarabine and 8 mg/kg Busulfan.

Background: The optimal regimen for allogeneic stem cell transplantation with a reduced-intensity conditioning regimen (RIST) needs to be established. Therefore, we retrospectively reviewed data of 84 patients who underwent RIST using 180 mg/sqm fludarabine and 8 mg/kg busulfan (Flu/Bu8). All patients received mobilized blood stem cells from a related donor between Nov. 2000 and Jun. 2005.

Patients and Methods: The median age of the patients was 53 years (range, 25–65). The diagnosis included 42 AML/MDS, 34 lymphoma and 8 others. Sixty-nine patients (82%) had high-risk diseases, including 56 (81%) in non-remission status before RIST. All were serologically 6/6 matched pairs, except for one who had a 5/6 match. For GVHD prophylaxis, 61 used cyclosporine A (CSP) alone, 21 used CSP + methotrexate (MTX), and 2 used some other compounds.

Results: The engraftment kinetics were remarkable since all of the patients successfully engrafted at a median of 11 days (5–24 days), with no late graft rejection. Toxicities of grade 2 or 3 according to CTCAE v.3 were observed at minimal frequencies, i.e. 38 mucosal, 35 hepatic, 13 GI tract, 12 renal, 2 cardiac, 1 pulmonary, 19 febrile neutropenia, and 9 documented infections, and there were no grade 4 toxicities. The administration of MTX increased the incidence and severity of stomatitis (P=0.05). The cumulative incidences of grade II–IV and III–IV acute GVHD were, respectively, 50% and 29%, and 76% experienced chronic GVHD. Seventy-three patients (87%), including 38 of the 56 patients who were not in CR at the time of transplant, achieved partial or complete remission. The median follow-up of surviving patients was 1349 days (34–1981 days), and the day-100 mortality was 11% (disease progression 6% and non-relapse mortality [NRM] 5%). The 5-year overall and progression-free survival rates were 36% and 30%, respectively. Among 46 total deaths, 27 were from disease progression and 19 were from NRM primarily related to GVHD. The patients in remission at transplant showed better overall survival than those who were not in remission (85 % vs 34 % at 5 years post-transplant, respectively, P<0.05). The 5-year overall survival was 85 % for those in remission at transplant and 34 % for the remaining patients (P<0.05). Multivariate analyses showed that age older than 52 years and non-CR status at transplant were associated with an increased risk for mortality after RIST.

Conclusions: Our study showed that RIST with this Flu/Bu8 regimen is feasible with durable engraftment and low early mortality. The clinical response rate is adequate for those who stayed in remission at transplantation, but otherwise a novel approach to prevent disease progression should be developed.