Outcome of Busulfan and Fludarabine-Based Reduced Intensity Conditioning Regimen for Related and Unrelated HSCT in Fanconi Anemia Patients
Authors: Azarnoush Saba , Porcher Raphael , de la Tour Regis Peffault , Yakouben Karima , Bruno Benedicte , Chardin Marie Ouachee , Robin Marie , Baruchel Andre , Socie Gerard , Dalle Jean-Hugues 
Published: October 2019

Abstract
Abstract 1964

Rationale:
HSCT is the only curative treatment for Fanconi Anemia (FA) pts with either bone marrow failure or MDS/Leukemia. Due to characteristic chromosomal instability, the poor outcome of FA pts transplanted after so-called conventional myelo-ablative conditioning regimen has been proved. Then, reduced-intensity conditionning regimen (RIC) has been considered for years as a model for allogeneic HSCT in FA pts. The use of fludarabine-based cond' regimen from about 2000 increased dramatically the overall survival of FA pts. Different Flu-based RIC were developed.
Patients and method: Between Feb'02 and Dec'10, 17 FA pts from 3 academic French centers were included: 11 from R. Debre hospital, 5 from St Louis hospital and 1 from J. de Flandre hospital. All pts underwent HSCT because of bone marrow failure. They presented no MDS or leukemia. All time-to-event outcomes were counted from the date of HSCT to the date of event or date of last follow-up, except acute GVHD that was arbitrarily censored at 200 days. Death was considered as a competing risk in analyses of neutrophil and platelet recovery and chronic and acute GVHD. Overall survival was estimated using Kaplan-Meier product-limit estimator. For competing risks analyses, cumulative incidences were estimated using usual methodology.

Results:
Median age at diagnosis and at HSCT were 4.7 years (range 1,8-9,3) and 7,4 years (range 4,4-15,2), respectively. 12 pts presented with less than 3 FA-related malformations and 5 with more than 3 malformations. 2 patients received more than 20 transfusions before HSCT, whereas 8 pts received less than 20 transfusions and 7 patients did not received any. 2 patients received androgen therapy before HSCT.
All patients received the same RIC i.e. fludarabine 30mg/m2/d × 3d, cyclophosphamide 10mg/kg/d × 4d and IV busulfan (Bu) 0.75 of body weight- adjusted recommended dose (equivalent to 6.4mg/kg total dose of oral Bu). This RIC did not contain any irradiation. Graft versus-host disease (GvHD) prophylaxis consisted of CSA associated with MMF or corticosteroids. Donors were either matched related (sibling, n= 6; other, n=2) or unrelated (10/10, n= 6; 9/10, n= 3). Stem cell sources were BM (n=10), UCB (n=4) and PBSC (n=2). 9 out of 17 pts had a donor from the same gender whereas 4 male recipients received transplant from female donor. CMV status were −/−, −/+, +/− and +/+ for 8, 4, 1 and 4 D/R pairs, respectively.
Median follow-up was 32 months (range 3–102).
Successful engraftment was obtained in all patients with a median time for neutrophil recovery of 17 days (range 10–42). All patients presented with 100% donor chimerism. One patient experimented secondary graft failure and died at D291 from infection and renal failure. During transplant procedure, 13 pts experimented at least one severe infectious complication (staphylococcus n=2; pseudomonas n=1; aspergillus n= 2; candida n=2; viral reactivation n= 13). 1 pt presented with moderate hepatic veno-occlusive disease. Five pts died from TRM and 12 pts remained alive in a good health condition. 36 month OS was 69% (95%CI 50 to 96). Cumulative incidence of grade 2 to 4 acute GVHD was 71% (95%CI: 41–87). 5 pts presented with either limited (n=4) or extensive (n=1) chronic GvHD and 36 month cumulative incidence of chronic GVHD was 33% (95%CI 11 to 58). To date, no pt had secondary malignancy.

Discussion:
Our study confirms the good results obtained by other groups when using flu-based RIC in FA pts. Indeed, satisfying engraftment and long-time survival rates were obtained without any TBI, irrespective of the stem cell source and the donor type. However, we have a concern regarding the cGVHD rate we obtained. As demonstrated by an on-going study of EBMT registry, the risk of secondary malignancy in these pts is statistically correlated to cGvHD. Then, this rate still remains probably too high in our study, even though only one pt presented with extensive cGvHD and no pts developed any secondary malignancy. But this could be explained by the short follow-up. Suppression of one alkalyting agent may reduce both cGVHD incidence and other tissue injuries leading to secondary malignancies. Then, we claim for suppression of Bu for related donor HSCT. In FA pts receiving transplant from unrelated donor, the relative impact of either low-dose IV-Bu – as we used here - or low-dose irradiation on toxicity and especially development of secondary malignancies remains to be evaluated.

Disclosures:
No relevant conflicts of interest to declare.