Conditioning for allogeneic transplantation in Aplastic Anemia

Stem cell Transplantation is the only curative therapy long term for Aplastic Anemia(AA). Before stem cells can be transfused, the marrow needs to be conditioned. In younger patients with Aplastic Anemia, the standard conditioning proposed by the Working Party(WPSAA) on AA is cyclophosphamide 50 mg/kg 32 × 4 + ATG. This regimen does not completely destroy the patient’s bone marrow and it is highly immunosuppressive in order prevent graft rejection and GVHD. Often ATG(Thymogen/ anti-thymocyte globulin)) for more immunosupression is also added. The benefit of adding ATG to cyclophosphamide is unclear, because a recently published prospective randomized clinical trial (RCT) from CIBMTR showed no significant benefit in terms of graft rejection, GVHD, and survival rates, compared with cyclophosphamide alone. Raw unadjusted data, from the EBMT database, however, show a slightly superior 10-year survival of 85% versus 75% when ATG is used as part of the conditioning regimen in sibling donor transplantation.

Patients older then 30 years of age, do less well with allogeneic transplantation because they tolerate GVHD less well. There is some support for using fludarabine, a more immunosupressive drug, for such patients. Fludarabine based conditioning regimen may reduce the negative impact of age in older patients receiving an HLA-identical sibling stem cell transplant  Alemtuzumab is a new drug that has been studied and that may also decrease the risk of Graft versus Host Disease. A recent European retrospective review of the combination of Fludarabine, cyclophosphamide and antithymocyte globulin(FCA), with or without low dose total body irradiation, concluded that TBI might have a role. The overall survival was quite comparable for the two regimens, though significant differences were found following more detailed analysis of subgroups. FCA conditioning regimen seems suitable for very young patients with well-matched donors; in other settings the addition of TBI 2 Gy to the FCA regimen seems to offer a better chance of cure, in keeping with results of other recent studies

There is no comparative information for any specific conditioning regimen in young adults with Aplastic Anemia. FCA is as well supported as other alternatives. For that reason, since stem cell transplantation is well established for Aplastic Anemia and the conditioning regimens are a part of this established procedure, the FCA regimen should not be considered Experimental or Investigational and it is medically necessary. The evidence for TBI is weak for young patients and TBI is experimental and it is not medically necessary.

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