Aplastic anemia is a rare hematologic disorder marked by pancytopenia and a hypocellular marrow. Aplastic anemia results from either inherited or acquired causes, and the treatment approach varies significantly between the 2 causes. This article reviews the treatment of inherited and acquired forms of aplastic anemia. The approach to evaluation and diagnosis of aplastic anemia is reviewed in a separate article.
Inherited Aplastic Anemia
First-line treatment options for patients with inherited marrow failure syndromes (IMFS) are androgen therapy and hematopoietic stem cell transplant (HSCT). When evaluating patients for HSCT, it is critical to identify the presence of an IMFS, as the risk and mortality associated with the conditioning regimen, stem cell source, graft-versus-host disease (GVHD), and secondary malignancies differ between patients with IMFS and those with acquired marrow failure syndromes or hematologic malignancies.
Potential sibling donors need to be screened for donor candidacy as well as for the inherited defect.1 Among patients with Fanconi anemia or a telomere biology disorder, the stem cell source must be considered, with bone marrow demonstrating lower rates of acute GVHD than a peripheral blood stem cell source.2-4 In IMFS patients, the donor cell type may affect the choice of conditioning regimen.5,6 Reduced-intensity conditioning (RIC) in lieu of myeloablative conditioning without total body irradiation has proved feasible in patients with Fanconi anemia, and is associated with a reduced risk of secondary malignancies.5,6 Incorporation of fludarabine in the conditioning regimen of patients without a matched sibling donor is associated with superior engraftment and survival2,5,7 compared to cyclophosphamide conditioning, which was historically used in matched related donors (MRD).6,8 The addition of fludarabine appears to be especially beneficial in older patients, in whom its use is associated with lower rates of graft failure, likely due to increased immunosuppression at the time of engraftment.7,9 Fludarabine has also been incorporated into conditioning regimens for patients with a telomere biology disorder, but outcomes data is limited.5
For patients presenting with acute myeloid leukemia (AML) or a high-risk myelodysplastic syndrome (MDS) who are subsequently diagnosed with an IMFS, treatment can be more complex, as these patients are at high risk for toxicity from standard chemotherapy. Limited data suggests that induction therapy and transplantation are feasible in this group of patients, and this approach is associated with increased overall survival (OS) despite lower OS rates than IMFS patients who present prior to the development of MDS or AML.10,11 Further work is needed to determine the optimal induction regimen that balances the risks of treatment-related mortality and complications associated with conditioning regimens, risk of relapse, and risk of secondary malignancies, especially in the cohort of patients diagnosed at an older age.
Acquired Aplastic Anemia
While the work-up and treatment plan is being established, attention should be directed at supportive care for prevention of complications. The most common complications leading to death in patients with significant pancytopenia and neutropenia are opportunistic infections and hemorrhagic complications.12
Transfusion support is critical to avoid symptomatic anemia and hemorrhagic complications related to thrombocytopenia, which typically occur with platelet counts lower than 10,000 cells/µL. However, transfusion carries the risk of alloimmunization (which may persist for years following transfusion) and transfusion-related graft versus host disease (trGVHD), and thus use of transfusion should be minimized when possible.13,14 Transfusion support is often required to prevent complications associated with thrombocytopenia and anemia; all blood products given to patients with aplastic anemia should be irradiated and leukoreduced to reduce the risk of both alloimmunization and trGVHD. Guidelines from the British Society for Haematology recommend routine screening for Rh and Kell antibodies to reduce the risk of allo-immunization.15 Infectious complications remain a common cause of morbidity and mortality in patients with aplastic anemia who have prolonged neutropenia (defined as an absolute neutrophil count [ANC] < 500 cells/µL).16-19 Therefore, patients should receive broad-spectrum antibiotics with antipseudomonal coverage. In a study by Tichelli and colleagues evaluating the role of granulocyte-colony stimulating factor (G-CSF) in patients with SAA receiving immunosuppressive therapy, 55% of all patient deaths were secondary to infection.20 There was no OS benefit seen in patients who received G-CSF, though a significantly lower rate of infection was observed in the G-CSF arm compared to those not receiving G-CSF(56% versus 81%, P value = 0.006).This difference was largely driven by a decrease in infectious episodes in patients with very severe aplastic anemia (VSAA) treated with G-CSF as compared to those who did not receive this therapy (22% versus 48%, P value = 0.014).20
Angio-invasive pulmonary aspergillosis and Zygomycetes (eg, Rhizopus, Mucor species) remain major causes of mortality related to opportunistic mycotic infections in patients with aplastic anemia.18 The infectious risk is directly related to the duration and severity of neutropenia, with one study demonstrating a significant increase in risk in patients with neutropenia lasting longer than 3 weeks in patients with AML.21 Invasive fungal infections carry a high mortality in patients with severe neutropenia, though due to earlier recognition and empiric antifungal therapy with extended-spectrum azoles, overall mortality secondary to invasive fungal infections is declining.19,22
While neutropenia related to cytotoxic chemotherapy is commonly associated with gram-negative bacteria due to disruption of mucosal barriers, patients with aplastic anemia have an increased incidence of gram-positive bacteremia with staphylococcal species compared to other neutropenic populations.18,19 This appears to be changing with time. Valdez and colleagues demonstrated a decrease in prevalence of coagulase-negative staphylococcal infections, increased prevalence of gram-positive bacilli bacteremia, and no change in prevalence of gram-negative bacteremia in patients with aplastic anemia treated between 1989 and 2008.22 Gram-negative bacteremia caused by Stenotrophomonas maltophila, Escherichia coli, Klebsiella pneumoniae, Citrobacter, and Proteus has also been reported.19 Despite a lack of clinical trials investigating the role of antifungal and antibacterial prophylaxis for patients with aplastic anemia, most centers initiate antifungal prophylaxis in patients with severe aplastic anema (SAA) or VSAA with an anti-mold agent such as voriconazole or posaconazole (which has the additional benefit compared to voriconazole of covering Mucor species).17,23 This is especially true for patients who have received ATG or undergone HSCT. For antimicrobial prophylaxis, a fluoroquinolone antibiotic with a spectrum of activity against Pseudomonas should be considered for patients with an ANC < 500 cells/µL.17 Acyclovir or valacyclovir prophylaxis is recommended for varicella-zoster virus and herpes simplex virus prophylaxis. Cytomegalovirus reactivation is minimal in patients with aplastic anemia, unless multiple courses of ATG are used.
Iron overload is another complication the provider must be aware of in the setting of increased transfusions in aplastic anemia patients. Lee and colleagues demonstrated that iron chelation therapy using deferasirox is effective at reducing serum ferritin levels in patients with aplastic anemia (median ferritin level: 3254 ng/mL prior to therapy, 1854 ng/mL following), and is associated with no serious adverse events (most common adverse events included nausea, diarrhea, vomiting, and rash).24 Approximately 25% of patients in this trial demonstrated an increase in creatinine, with patients taking concomitant cyclosporine more affected than those on chelation therapy alone.24 For patients following HSCT or with improved hematopoiesis following immunosuppressive therapy, phlebotomy can be used to treat iron overload in lieu of chelation therapy.15