Effect of Race on Outcomes After Allogeneic Hematopoietic Cell Transplantation for Severe Aplastic Anemia

Abstract 1020

Severe aplastic anemia (SAA) is the most common non-malignant indication for hematopoietic cell transplantation (HCT). Although survival after HCT for SAA has improved in recent years, it is not known whether the observed higher survival rates are uniform across racial groups or whether there are differences similar to those seen with HCT for hematologic malignancies. Our primary objective was to compare overall survival after HCT for SAA in patients of African American and Caucasian races. The study population included patients who received HCT in the U.S. between 1990 and 2008. Eighty-four African Americans (cases) and 215 Caucasians (controls) were matched on factors known to be associated with survival after HCT for SAA, including age at HCT (±3 years), donor type (HLA-matched sibling, matched unrelated donor, mismatched unrelated donor), graft type (bone marrow or peripheral blood progenitor cells) and transplant year (±1 year). For 39 cases the match ratio for controls was 1:4, for 14 cases, 1:3, for 22 cases, 1:2 and the remaining 9 cases, 1:1. The median age of cases and controls was 17 years and the median interval from diagnosis to HCT was 3.4 months. Forty-five percent of transplants were from unrelated and 55% from HLA-matched sibling donors. A third of unrelated donor-recipient pairs were HLA-mismatched. Bone marrow was the predominant source of stem cells. The median follow-up of cases and controls was 5 years. In multivariate analysis, risk of overall mortality was higher for African Americans compared to Caucasians, relative risk [RR] 1.75, 95% CI 1.14–2.69, p=0.01. Risks of overall mortality were also higher during the early post-transplant period; odds ratio (OR) 2.42, 95% CI 1.09–5.37, p=0.03) and OR 2.61, 95% CI 1.33–5.47, p=0.005) at 3-months and 1-year post-transplantation, respectively. The 5-year probability of overall survival adjusted for interval from diagnosis to HCT, performance score and conditioning regimen, the other significant variables associated with higher mortality was 58% for African Americans and 73% for Caucasians. The likelihood of neutrophil recovery was similar in both groups (OR 1.03, 95% CI 0.46–2.33, p=0.94). Acute grades II–IV graft-versus-host disease (GVHD) risks did not differ between African Americans and Caucasians (RR 0.81, 95% CI 0.56–1.17, p=0.26). However, chronic GVHD risk was higher for African Americans, although the difference did not reach statistical significance (RR 1.55, 95% CI 0.98–2.44, p=0.06). Thirty-seven (45%) of 82 African Americans died compared to 56 (27%) of 207 Caucasians. The proportion of patients dying with GVHD was higher in African Americans (12 of 37; 32%) than among Caucasians (9 of 56; 16%). Death secondary to organ failure was higher in Caucasians (12 of 56; 26%) compared to African Americans (4 of 37; 11%). There were no differences between African Americans and Caucasian in regards to deaths from graft failure, infection or hemorrhage. These data suggest recent improvements in overall survival rates after HCT for SAA are largely limited to Caucasians. Higher mortality in African Americans may be explained by greater genetic diversity, which renders the identification of donors by high-resolution HLA-typing more challenging, genetic polymorphisms impacting drug metabolism and unmeasured co-morbidities. Novel strategies aimed at lowering acute and chronic GVHD rates are needed to lower GVHD-related deaths.