Fludarabine Is Superior to Cladribine When Added to Busulfan and Low Dose TBI as Reduced Intensity Conditioning for Allogeneic Hematopoietic Cell Transplantation (HCT): A Prospective Randomized Trial.

Purine analogues have been combined with alkylator/irradiation as immunosuppressive and anti-tumor conditioning prior to allogeneic hematopoietic stem cell transplantation (HCT) though differing purine analogues have not been compared. We prospectively tested Fludarabine (F) 40 mg/m2/d x 5d vs. Cladribine (C) 10 mg/m2/d x 5d plus Busulfan (Bu) (2mg/kg q12h x 2d) and total body irradiation (T) 200cGy followed by cyclosporine and mycophenylate mofetil in 19 recipients of matched sibling peripheral blood stem cell and 13 unrelated donor (URD) marrow HCT. Patients in each randomly assigned cohort [FBuT vs. CbuT] were similar in age (median 52 years in both groups), diagnosis (leukemia/MDS 38 vs. 31%; lymphoid malignancy 57 vs 69%), extensive pre-HCT therapy (56 vs. 63%), high risk disease status (81 vs. 93%) and Karnofsky (median 90 in each)[all p= NS] though fewer FBuT were URD recipients 25% vs. CBuT 56%, p=0.07. Engraftment was prompt in both groups (median 11 vs. 12 days), but the cumulative incidence of neutrophil engraftment was 75% (95% C.I. 54–96%) using CBuT vs. 100% with FBuT (p<0.01) and randomization was halted. Platelet recovery was prompt (median FBuT 18 vs CBuT 24 days) and after FBuT 75% (95% C.I. 49–100) vs. CBuT 69% (43–95) recovered platelets > 50,000/μL by day +180, p=0.19. The cumulative incidence of GVHD after FBuT vs. CbuT was similar (acute grade II/IV 56 vs. 69%, p=0.26) and (chronic 50 vs. 31%, p=0.27). Transplant related mortality at day +180 was also similar [FBuT 25% (4–46) vs. CbuT 38% (14–61), p=0.47]. Survival was equivalent: at 1 year 50% in each group; at 3 years FBuT 25% vs. CBuT 38%, p=0.55. Multivariate analyses adjusted for age, donor type, diagnosis and stage as well as conditioning regimen showed lower relative risk (RR) of engraftment with CBuT (RR 0.6 (95% C.I. 0.2–1.3) p=0.16) and with URD RR 0.4 (0.2–1.0) p=0.04). RR of Platelet recovery was equivalent with FBuT (RR 0.7 (0.3–1.7) p=0.45) but inferior with URD (RR .16 (.05–.5) p<0.01). RR of GHVD II/IV similar with FBuT RR 1.1, p=0.95, but more frequent with URD RR 2.0, p=.2 and high risk status patients (RR 4.5, 1.5–13.5, =<0.01). Prevalence of remission (CR or PR) at 18 months was high and was similar in both groups (FBuT 100% vs CBuT 86%, p=NS). These data suggest that older patients with advanced hematologic malignancies can achieve satisfactory post-transplant outcomes using either of these combination/reduced intensity conditioning regimens. Fludarabine may be superior to cladribine as a component of pre-HCT conditioning with Bu/TBI due to reduced risks of graft failure. Further modifications of the regimen may confirm universal engraftment with even lower peri-transplant morbidity.