Introduction
Allogeneic hematopoietic stem cell transplantation (alloSCT) represents a curative therapy for various malignant and non-malignant hematological diseases [
1]. However, despite improvement, its success is still limited by its high toxicity. Around 20–32% of the patients die in consequence of non-relapse mortality (NRM) [
2‐
4]. Predominant reasons are lethal infections, organ failure, and both acute and chronic graft-versus-host disease (GvHD) [
5,
6]. Established risk factors for NRM include age [
4,
7] and comorbidities [
8] as well as conditioning intensity in older patients [
9,
10]. The most common score used to assess the NRM risk is the HCT-CI score [
11]. Despite the fact that alloSCT causes relevant metabolic changes [
12] with an estimated increased basal metabolic rate of 130–150% [
13] and that a deficient nutritional state is associated with worse outcome [
14], the HCT-CI contains only one nutrition-related parameter which is obesity, i.e., a body mass index (BMI) of > 35 kg/m
2. However, there is conflicting evidence from different trials on the impact of obesity on alloSCT outcomes and NRM risk, and therefore the relevance of the BMI is still disputed [
15‐
19].
Given its impact on organ function and immune response, a number of studies have explored nutrition-associated parameters in the setting of alloSCT; however, little data exist on their exact role in NRM [
20] and no verified and easily accessible parameter for nutritional status monitoring specifically in the alloSCT setting has been established.
Possible parameters include weight as well as BMI or its categories based on WHO standards [
21,
22]. Regarding an association of BMI prior to SCT with outcome conflicting results have been reported. Various studies show reduced survival for patients with obesity [
15], while other studies did not support this finding [
16‐
18]. There is agreement on a general reduction of BMI post-SCT [
23‐
26], but data on the relevance of BMI change in the post-SCT course have only scarcely been analyzed.
Other parameters related to the nutritional status are serum total protein and serum albumin. For both association with outcome has been reported for different hemato-oncological entities, e.g., peripheral T-/NK-cell lymphomas [
27]. A prognostic relevance for SCT has been suggested, but is disputed [
28,
29].
A better understanding of nutrition particularly in the post-SCT course and its relevance for NRM may not only aid in assessing prognosis but also in designing interventions to improve outcome. The benefit of such interventions has been discussed, but data remain unclear [
30,
31].
Given the sparse data particularly on the relevance of post-SCT nutritional status, we evaluated the association of nutritional status assessed by BMI, serum total protein, and albumin at different time points prior and after alloSCT with NRM-related outcome.
Discussion
Our present study belongs to the small number of studies analyzing nutrition-related data not only prior to alloSCT but also in the post-SCT course and in specific relation to NRM rather than overall survival (OS). In our single-center cohort, which comprised a typical distribution of donor, recipient, and transplant characteristics, we observed no association of BMI or its alterations in the post-SCT course with NRM. In contrast, serum albumin deficiency prior to SCT as well as at d+30 and d+100 post-SCT was consistently associated with NRM in multivariate analysis. While BMI, serum total protein, and serum albumin decreased in the post-SCT course, this decrease did not correlate with NRM.
Concerning the association between pre-SCT BMI and the outcome of allogeneic SCT, current data are inconsistent and comparability is hindered by different cut-offs of categorized BMI. Our finding of pre-SCT BMI being not associated with NRM is supported by other studies [
16,
19], suggesting that neither underweight nor obesity prior to allogeneic SCT effect patients’ outcome. Due to the rising prevalence of adiposity, many studies focused on the impact of obesity on safety and efficacy of allogeneic SCT. In a retrospective analysis of CIBMTR data, Navarro et al. reported a comparable outcome of AML patients with a BMI ≥ 30 kg/m
2, including OS [
18]. These results were confirmed in obese (BMI ≥ 30 kg/m
2) elderly patients (≥ 60 years) who underwent allogeneic SCT for myeloid malignancies and whose outcome including OS and progression-free survival were not affected by obesity [
34].
Conversely, other authors reported an association of pre-SCT BMI with NRM-related survival [
15,
17,
35,
36]. In a large cohort of 2503 adult patients, Doney et al. showed that both underweight (BMI ≤ 18.5 kg/m
2) and very obese (BMI ≥ 35.0 kg/m
2) patients had an increased NRM and underweight patients also had an elevated relapse and overall mortality rate [
15]. In the retrospective analysis performed by Fuji et al. with registry data of 12,050 patients, NRM was significantly higher in the overweight and obese group (BMI ≥ 25.0 kg/m
2) compared with the normal BMI group, mainly due to an increased GvHD- and infection-related NRM. However, this did not translate into a decreased overall survival for this patient group due to an increased risk of relapse in patients with a BMI ≤ 18.5 kg/m
2 [
35]. The study of Gleimer et al. showed the same association with a higher NRM in obese patients (BMI ≥ 30.0 kg/m
2), yet no difference in OS due to a lower incidence of relapse in the obese patient group. NRM was mainly caused by acute and chronic GvHD, but despite a trend towards a higher incidence of both acute and chronic GvHD in obese patients, no difference compared to normal weight patients was shown [
36]. Given the limited size of our cohort, we did not include GvHD as an additional covariate in our analysis.
The data reporting a higher NRM for obese patients are reflected in the addition of obesity defined by a BMI > 35 kg/m
2 to the relevant comorbidities in the HCT-CI score, which is used for predicting transplant-related mortality risk prior to allogeneic SCT [
11].
In a longitudinal analysis, we showed similar to other authors a relevant weight loss represented by a decrease of BMI over the course of alloSCT. Due to the intensity of the treatment, this finding is expected and has been confirmed in other studies [
25,
26,
37]. The retrospective study by Rieger et al. compared patients’ weight at the time of hospital admission for alloSCT, discharge (median 41 days after alloSCT), and at the end of follow-up, which was 873 ± 361 days after transplant [
37]. There was no difference between the medium BMI at these time points, providing a comparable cohort to our study with a medium follow-up of 1 year. Surprisingly, in our study, patients without a reduction in BMI after
d+30 showed an increased NRM; however, this finding did not remain significant in multivariate analysis and may thus be related to other factors. For instance, other studies showed an association of GvHD with a BMI reduction [
24,
26]. This was confirmed by Rieger et al., observing no meaningful difference in overall survival between patients with or without substantial weight loss. This data is contradicted by a study of Fuji et al., reporting a worse outcome (NRM and OS) of patients with a weight loss ≥ 10% after alloSCT [
38].
Overall, the effect of pre-SCT BMI and its course after SCT on the outcome of SCT remains unclear. Different institutional practices of chemotherapy dose modifications according to actual or adjusted body weight as well as internal guidelines on nutritional support further reduce the comparability of the data. In addition, BMI might not represent a suitable marker for describing the nutritional status of a patient, since it does not differentiate between excess body fat, muscle mass, or surplus water. Due to the retrospective design of our study, no further analyses of patients’ body composition, e.g., by bioelectric impedance analysis, which allows an estimation of human body composition, especially body fat and muscle mass, were possible. Yet, since weight remains one of the few patient-related factors that can be influenced by reasonable interventions prior to SCT, further studies are needed to evaluate its impact.
One parameter that may represent the nutritional status of the patients more accurately is serum albumin. In our cohort, serum albumin pre-SCT as well as at 30 and 100 days after SCT was significantly associated with NRM and particularly a severe albumin deficiency (< 28 g/l) correlated strongly with a higher NRM risk. Various studies have shown that serum albumin levels both prior to SCT [
39,
40] and in the post-SCT course [
41,
42] correlate with outcome of SCT. Although different classifications and cut-offs for hypoalbuminemia limit the comparability of these studies, low serum albumin has been consistently associated to an increased NRM, and therefore the addition of this parameter to the HCT-CI score (“Augmented HCT-CI”) has been suggested and retrospectively validated [
43,
44]. A possible explanation for this observation is the higher susceptibility towards and worse outcome of complications after allogeneic SCT in patients with hypalbuminemia, such as invasive fungal infections [
45] and acute GvHD [
46,
47].
Additionally, our present study for the first time to our knowledge shows that the further decrease of albumin levels in the post-SCT course is not relevant for NRM. We therefore reason that primarily albumin deficiency prior to SCT is a prognostic factor predicting increased NRM risk. This is relevant, as many other factors common in the SCT and post-SCT course influence albumin levels, e.g., hydration and sepsis [
48,
49]. While low serum albumin levels are well-recognized markers of both nutritional status and liver function, it also serves as a surrogate parameter for chronic inflammation processes [
50]. Among other laboratory indicators, lower albumin is associated with disease activity in patients with chronic GvHD [
51]. In patients undergoing an allogeneic SCT, and therefore an intensive immunotherapeutic treatment characterized by extensive immune and inflammatory processes in the course of engraftment and further follow-up, this emphasizes the clinical relevance of pre-SCT albumin levels and underlines the difficulty of evaluating albumin levels during the course of the treatment.
In contrast to others [
42], we have not found an association of serum total protein levels with NRM. In a multivariate analysis in a cohort of patients surviving 100 days after alloSCT, Wojnar et al. identified low serum total protein (< 60 g/l) on day + 100 after allogeneic SCT as an independent risk factor for NRM. The authors suggested that low serum total protein may reflect most of the complications common about 3 months after SCT, including impaired liver function as part of both acute and chronic GvHD as well as infections, malabsorption, and low immunoglobulin levels, which may additionally contribute to an elevated risk of potentially lethal infections [
42]. Additionally, in a retrospective analysis by Ferreira et al., a positive correlation between serum total protein level at discharge and survival time after alloSCT was shown; yet, the influence on NRM was not analyzed [
52].
In our cohort, both low serum total protein pre-SCT and on
d+100 after SCT were associated with increased NRM in univariate analysis. However, this correlation was not confirmed in multivariate analysis. These findings are supported by Dietrich et al., who showed that low serum total protein (< 70 g/l) is a strong predictor of relapse in patients undergoing allogeneic SCT for AML, but has no impact on NRM [
28].
Overall, data on the impact of pre-SCT serum total protein on the outcome of SCT is very limited, possibly due to its limited ability in reflecting patients’ nutritional status as it comprises many different serum proteins, including acute phase proteins and other short-lived proteins. In our cohort, only pre-SCT albumin, but not serum total protein was confirmed as a predictive marker of NRM in multivariate analysis. Yet, when assessing the nutritional status of patients, nutrition-associated blood parameters are influenced by diverse (individual) factors and are subject to their own restrictions. In the setting of allogeneic SCT especially, edema needs to be considered for BMI evaluation and stress, infections, organ dysfunctions, and gastrointestinal symptoms for evaluation of blood parameters [
25,
48,
49,
53]. Therefore, nutrition-associated parameters must always be interpreted in the clinical context of the individual patient.
In sum, it is apparent that nutritional parameters and status influence the outcome after allogeneic SCT. Since the nutritional status can be modified through nutritional support, the implementation of nutritional guidelines for patients during and after allogeneic SCT should be an essential component of clinical practice. In a survey among German, Swiss, and Austrian transplant centers, all centers stated that they had established nutritional guidelines for their patients undergoing alloSCT; yet, the clinical implementation of nutritional support was very heterogenous [
54]. Therefore, more data are required to facilitate the development and implementation of evidence-based nutrition guidelines for patients undergoing alloSCT.
Our present single-center cohort study was limited by its retrospective design. Moreover, its heterogeneous cohort with a relatively small number of patients limited the interpretation of the results, especially in the subgroup analyses. Given our findings, larger studies and prospective trials are needed to confirm the adverse effects of pretransplant malnutrition and determine whether improving the nutritional status prior to alloSCT by an adequate pretransplant nutritional support would lead to an improved outcome.
Our findings of serum albumin deficiency both prior to SCT as well as post-SCT being associated with NRM after allogeneic SCT may not only add to the risk evaluation and counseling of patients but may also serve as a rational for early monitoring and interventions to improve the nutritional status in at-risk patients starting prior to SCT.
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.