Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for acute leukemia (AL). Despite the reduction in transplant-related risk during the last few years, it is still associated with significant morbidity and mortality, which raises the question of who, how and when to transplant.

Transplant-related mortality (TRM) is mainly due to graft-versus-host disease (GVHD), infection and organ toxicity. Several factors are known to affect TRM and survival among HSCT patients, such as those related to the patient (e.g., age and comorbidities), baseline disease (e.g., disease stage at the time of transplant and cytogenetic features), donor (i.e., human leukocyte antigen (HLA) match between donor and recipient) and the procedure itself (e.g., type of conditioning regimen).1–3 Since TRM differs considerably among HSCT recipients, a prognostic scoring system which can potentially guide patient counseling and clinical decision-making is strongly advised before proceeding to transplant.

Different scoring systems have already been devised for predicting HSCT outcomes, including the European Society for Blood and Marrow Transplantation (EBMT) risk score and the Hematopoietic Cell Transplantation-Comorbidity Index (HCT-CI).2,4 Although such scores do help in the clinical decision-making process, their predictive ability varies widely across different settings.2,4-6

In 2015, Shouval et al.7 developed and validated the Acute Leukemia – EBMT (AL-EBMT) score for the prediction of mortality following HSCT. This prognostic model comprised 10 variables related to the patient, donor, type of transplant, type of leukemia, disease stage at the time of transplant, year of transplantand annual HSCT center activity. In this study, the AL-EBMT score provided an individualized estimate of the probability of mortality within the first 100 days post-transplant in AL patients. It was also shown to be capable of predicting overall survival (OS), event-free survival (EFS-2) and TRM at 2 years after HSCT.7,8

Therefore, we proposed to evaluate the ability of the AL-EBMT risk score in predicting the 2-year OS, EFS and TRM in AL patients undergoing an HSCT at a reference transplant center in Brazil.

Seventy-nine patients were included, 44 (55.7%) of whom were male and the median age was 38 years (IQR: 27–47). AML was the most common diagnosis, accounting for 54 (68.4%) cases. Approximately a quarter (27.8%) of the AL cases were at an advanced stage (i.e., > CR2) at the time of transplant. All allogeneic transplants were HLA-matched, wherein familial donors accounted for the majority (77.2%) of cases. Stratification according to the AL-EBMT score into low-, intermediate- and high-risk groups yielded 32 (40.5%), 10 (12.7%) and 37 (46.8%) patients in each of the groups, respectively. These and other patient characteristics are shown in Table 1.

The estimated rate of OS-2 was 36.7% (95%CI: 26.2–47.2%). When stratified according to the AL-EBMT score, low-, intermediate- and high-risk groups had an estimated OS-2 of 50.0% (95%CI: 31.9–65.7%), 40.0% (95%CI: 12.3–67.0%), and 24.3% (95%CI: 12.1–38.8%), respectively; p = 0.01 (Figure 1). Comparison of low versus intermediate/high and of high versus low/intermediate AL-EBMT scores showed an OS-2 HR of 0.42 (95%CI: 0.22–0.78; p = 0.006) and 2.14 (95%CI: 1.22–3.76; p = 0.007), respectively (Table 2).

Figure 1.

Global survival curve in two years according to the AL-EBMT score in cohort of HC-UFMG.

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The estimated rate of EFS-2 was 32.3% (95%CI: 21.3–43.8%). When stratified according to the AL-EBMT score, low-, intermediate- and high-risk groups had an estimated LFS-2 of 42.9% (95%CI: 23.2–61,2%), 40.0% (95%CI: 12.3–67.0%), and 21.5% (95%CI: 9.0–37.5%), respectively; p = 0.04 (Figure 2). Comparison of low versus intermediate/high and of high versus low/intermediate AL-EBMT scores showed an EFS-2 HR of 0.42 (95%CI: 0.22–0.78; p = 0.006) and 2.10 (95%CI: 1.20 - 3.69; p = 0.009), respectively (Table 2).

Figure 2.

Leukemina-free survival curve in two years according to the AL-EBMT score in cohort of HC-UFMG.

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The estimated cumulative incidence of TRM-2 was 35.4% (95%CI: 25.5–46.0%). When stratified according to the AL-EBMT score, low-, intermediate- and high-risk groups had an estimated TRM-2 of 21.9% (95%CI: 9.4–37.6%), 30.0% (95%CI: 6.2–59.4%), and 48.6% (95%CI: 31.5–63.8%), respectively; p = 0.05 (Figure 3). Comparison of low versus intermediate/high and of high versus low/intermediate AL-EBMT scores showed a TRM-2 HR of 0.39 (95%CI: 0.17–0.91; p = 0.03) and of 2.47 (95%CI: 1.15–5.28; p = 0.01), respectively (Table 2).

Figure 3.

Cumulative incidence of transplant-related mortality in the first two years according to the AL-EBMT score in cohort of HC-UFMG.

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In this single-center, prospective cohort study, the AL-EBMT score proposed by Shouval et al.7 was shown to be seemingly applicable as a prognostic model for OS, LFS and TRM at two years post-HSCT in patients with AL, based on specific, assessable risk factors at the time of transplantation.

In their original, retrospective analysis of EBMT registry data on 28,236 adult patients who had been submitted to a first allogeneic HSCT for AL, Shouval et al.7 showed that the AL-EBMT score was able to provide a reasonable estimate of OS, LFS, and TRM in such patients. As in our study, most patients had AML (68% vs. 70%, respectively), with a similar proportion of disease at an advanced stage at the time of transplantation (28% vs. 21%) and of use of PBSC (78.5% vs. 78.3%, respectively). However, the study by Shouval et al.7 showed a greater proportion of unrelated donors (46.1% vs. 22.8% in ours) and less CMV seropositivity in the recipient (64.5% vs. 88.6%). Moreover, in their study, a more homogeneous distribution of the study population among the three AL-EBMT strata was observed; in the present study, a clear polarization between low-score (33% vs. 40.5% in our study) and high-risk (34.3% vs. 46.8%) categories was noted. This may at least partly explain the statistically significant results regarding the OS, LFS and TRM observed between these two categories in our study, as opposed to the absence of a significant discrimination between these two strata and the intermediate-risk category.

In a second, retrospective, multicenter, the Gruppo Italiano Trapianti di Midollo Osseo (GITMO) cohort study aiming to validate the AL‐EBMT score for the prediction of mortality following allogeneic HSCT by stratifying 1848 patients according to the previously mentioned risk categories,8 this prognostic model was shown to provide a reasonable estimate of the OS, LFS, and TRM both in the short-term (100 days post-HSCT) and at 2 years post-transplant. Compared to our study, that of Shouval et al. showed a similar predominance of patients with AML (68.4% and 68.1%, respectively) and CMV seropositivity (88.6% and 81.4%), but a higher proportion of AML in CR1 (46.9% vs. 60.4%) and of unrelated donor transplants (22.8% vs. 49.6%); in contrast, lesser use of PBSC (69.9% vs. 78.5%) was noted, when compared to that in the current study (Table 3). As in the EBMT study, about a third (32%) of the patients in the AL-EBMT cohort were stratified as high-risk, as compared to almost half (46.8%) the patients in our cohort. As mentioned before, given the low representativeness of our study sample with respect to the intermediate-risk stratum (only 14.5% of the patients), this may account for the fact that significant discrimination was only observed between the lower and higher risk categories in our study.

Compared with other prognostic scores used in HSCT, Shouval et al.8 demonstrated that the AL-EBMT and the Hematopoietic Cell Transplant- Comorbidity Index (HCT-CI) were independent predictors of the OS, LFS and non-relapse mortality (NRM). Of note, in their study, the AL-EBMT index was shown to provide a better estimate of the OS and LFS, while the HCT-CI seemed more effective in stratifying NRM between each score. Therefore, we believe these prognostic models may serve as a complement to another, given their additive properties. By providing a weighted account of a myriad of clinically relevant risk factors comprised within the HSCT scenario, including baseline-disease, transplant, and patient-related characteristics, such scoring systems, once used together, may better refine the clinical decision-making process prior to HSCT in adult patients with AL.

Our study has some important limitations. This was not a validation study, but a preliminary study aimed at evaluating the feasibility and applicability of the AL-EBMT score in adult patients with AL in a developing country. Its unicentric nature and relatively small sample size hamper any definitive conclusions regarding the robustness and generalizability of our results. In addition, the unbalanced baseline characteristics observed in our study may have contributed to the polarization noted between low- and high-risk AL-EBMT groups (the vast majority of the patients had AML as the underlying disease, PBSCs as the stem cell source, MAC as the preparative regimen, CMV seropositivity among donor-recipient pairs, high overall performance status and a predominance of related donors).

On the positive side, this is one of the first studies using prospective data to analyze the applicability of the AL-EBMT score in an underserved country, such as Brazil. We were able to demonstrate the feasibility and applicability of this score in this population, with results that may be potentially reproducible across other transplant centers.

The AL-EBMT score is a simple and freely available tool comprised of readily assessable variables, which makes it an important and useful clinical tool for the risk assessment of patients with AL referred to HSCT. Larger, multicenter studies combining other risk indices, such as the HCT-CI, and other transplant scenarios (e.g., haploidentical transplants) are strongly encouraged to better evaluate its predictive role and usefulness in clinical decision-making in the HSCT setting. The ease in its use and apparent reliability may favor its widespread applicability across centers worldwide.