Real-World Outcomes with Immunosuppressive Therapy for Aplastic Anemia in Patients Treated at the University of Michigan
Authors: Foley Daniel H. , Foucar Charles E. , Pettit Kristen M. , Burke Patrick W. , Benitez Lydia L. , Perissinotti Anthony J. , Marini Bernard L. , Bixby Dale L. 
Published: November 2021

Abstract
Introduction
Aplastic anemia is a challenging disease to treat due to its rarity and severity. The current standard of care for severe and very severe aplastic anemia includes consideration of frontline allogeneic stem cell transplant (ASCT) in patients who are under 40 years of age and have an HLA-matched sibling. For patients who do not meet this criteria, immunosuppressive therapy (IST) consisting typically of horse antithymocyte-globulin (ATG) and cyclosporine (CsA) is considered, with recent data supporting the addition of eltrombopag. The main risks of IST are infusion reactions, serum sickness, kidney injury, and infection. While it is generally well tolerated in younger patients, older patients have historically been treated with transfusion support alone due to concerns for higher complications. Unfortunately, data to support clinical decisions regarding these concerns is limited, with small studies showing that reduced dosing or attenuated doses of ATG with or without CsA is safe and can be effective. At the University of Michigan, we have been treating older patients with attenuated doses of ATG +/- CsA since the late-2000s and have recently added eltrombopag to our standard of care. Herein, we present the results of our experience using IST to treat aplastic anemia, specifically presenting our outcomes in patients over 60 years old at the time of initiation of IST.
Methods
We used the Electronic Medical Record Search Engine (EMERSE) to query patients with aplastic anemia who were treated at the University of Michigan between 1995 and 2021. Patients included in our analysis were diagnosed with idiopathic aplastic anemia or hepatitis-associated aplastic anemia, were 18 years or older at the date of initiating IST, were treated with IST first-line, had adequate physician follow up at the University of Michigan, and were reported as being complaint with IST. Patients diagnosed or with high concern for hypoplastic myelodysplastic syndrome (MDS) were excluded in addition to those who received treatment for paroxysmal nocturnal hemoglobinuria (PNH). Statistical analysis was performed using SPSS Statistics v.27 (IBM, 2020).
Results
We identified 62 patients aged 18 - 60 and 54 patients over 60 years old who met inclusion criteria. Descriptive statistics of the two cohorts are available in Table 1. All patients in our study received horse ATG in addition to cyclosporine. 63% of patients over 60 received full dose horse ATG (20mg/kg for 5 days) and 37% received attenuated horse ATG (20mg/kg for 5 days), while 46% received eltrombopag as part of their IST. OS was superior in patients 18-60 receiving IST with median OS NR vs. 2760 days (Figure 1; p=0.009). In patients over 60, no difference in OS was observed in those who received attenuated (3646 days) vs. full dose IST (2760 days) (Figure 2, p=0.83). Lastly, no difference in median OS was seen in patients &gt; 60 years old who received eltrombopag compared to those who did not (2821 vs 2760 days, Figure 3, p=0.795).
Using a Chi-squared test, no statistically significant differences in rates of PR at 12 months, CR at 12 months, primary refractory disease, febrile neutropenia within 6 months of IST, bacterial infections within 6 months IST, and viral infections within 6 months of IST were noted between those who received dose attenuated ATG and those who received full dose ATG in patients &gt; 60. PR in older patients was 48% (12) and 36% (9) at 3 and 12 months with eltrombopag, compared to 40% (10) and 36% (9) without. CR in older patients was 12% (3) and 16% (4) with eltrombopag at 3 and 12 months, compared to 12% (3) and 12% (3) without. In patients &gt; age 60 who received dose attenuated IST, the addition of eltrombopag did not affect OS (Figure 4). A trend toward better OS was seen in patients 18-60 who received eltrombopag, but this was not statistically significant (Figure 5).

Discussion
In conclusion, we present our experience using IST to treat aplastic anemia at the University of Michigan. Dose attenuated IST has been proposed as a potential option for elderly patients, but we found no significant difference in OS, rates of response, or rates of infection between patients who received full dose and those who did not. There was also a trend toward improved survival with the addition of eltrombopag in younger patients, but additional follow up time is needed.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.