Allogeneic versus autologous transplantation in multiple myeloma: reduced relapse at the cost of higher non-relapse mortality in a large single-center cohort.

Introduction

Multiple myeloma (MM) is a clonal plasma cell malignancy that remains a significant therapeutic challenge in hematology [ 1 ]. As the second most common hematologic cancer, it accounts for approximately 1.8% of all global cancer diagnoses and is associated with substantial morbidity and mortality, with over 155,000 new cases and 100,000 deaths annually [ 2 – 4 ]. While the introduction of novel agents has markedly improved outcomes, the disease is still largely considered incurable, with a median survival typically ranging from 7 to 10 years in contemporary standard-risk cohorts [ 5 ]. This reality underscores the critical need for continued optimization of treatment strategies, particularly for achieving durable long-term control.

For decades, high-dose chemotherapy followed by autologous hematopoietic stem cell transplantation (ASCT) has been a cornerstone of first-line treatment for eligible patients with newly diagnosed MM. ASCT consistently delivers significant improvements in progression-free survival (PFS) and, in many studies, overall survival (OS) [ 4 ]. Its efficacy is well-established, particularly in younger patients with standard-risk disease [ 5 ], and it remains a viable and effective modality even in the era of modern induction therapy [ 4 , 6 , 7 ].

In contrast, the role of allogeneic hematopoietic stem cell transplantation (allo-SCT) in MM has been more controversial and has declined over the past decade [ 8 – 10 ]. This is primarily due to its association with substantial treatment-related risks, including graft-versus-host disease (GvHD), infection, and significant non-relapse mortality (NRM). Furthermore, the rapid development of highly effective novel immunotherapies, such as bispecific antibodies and chimeric antigen receptor T-cell (CAR-T) therapy, has provided alternative options for high-risk and relapsed disease [ 11 ]. Consequently, allo-SCT is now generally reserved for selected high-risk patients, although this selection has varied widely across institutions and treatment eras, often those without access to clinical trials of novel agents or who experience early relapse after ASCT.

Despite these challenges, the potent graft-versus-myeloma effect offered by allo-SCT presents a potentially powerful mechanism for achieving long-term disease control or even cure, a benefit rarely seen with ASCT alone [ 8 ]. This creates a complex risk-benefit calculus: the prospect of deeper, more sustained remission with allo-SCT must be carefully weighed against its higher procedural toxicity.

Given this ongoing debate, the paucity of real-world data with extended follow-up, and the evolving therapeutic landscape, we conducted this large, single-center retrospective study to compare the long-term outcomes of allo-SCT with the standard ASCT in a real-world cohort of MM patients, with a specific focus on survival, relapse incidence, and non-relapse mortality.

Methods

Study design and ethics approval

This retrospective, single-center study included 1,342 consecutive patients with multiple myeloma undergoing hematopoietic stem cell transplantation at our institution between October 1992 and October 2022, with follow-up through October 1, 2024. Given the long study period, treatment strategies, induction regimens, and supportive care evolved substantially over time.

Given the retrospective design and the use of anonymized clinical data collected as part of routine clinical care, formal prospective approval by an Institutional Review Board (IRB) or named Ethics Committee was not required at the time of patient treatment. All procedures were performed in accordance with the ethical standards of the institutional and national research committees and with the principles of the Declaration of Helsinki. Written informed consent for transplantation was obtained from all patients according to institutional standards of care.

Wherever available, baseline disease characteristics were extracted from medical records, including hemoglobin level, serum creatinine, serum albumin, lactate dehydrogenase (LDH), presence of osteolytic bone lesions, time from diagnosis to transplantation, and type and number of induction therapy cycles.

International Staging System (ISS) stage and presence of osteolytic bone lesions was available for a subset of patients but was incomplete and therefore not included in comparative analyses.

Treatment protocol and transplant eligibility

All newly diagnosed patients received induction therapy with a triple-drug regimen containing a proteasome inhibitor, an immunomodulatory drug (IMiD), and dexamethasone for four cycles. Eligibility for autologous transplantation (ASCT) required an age of up to 70 years, attainment of at least a very good partial response (VGPR), and adequate organ function, including a left ventricular ejection fraction ≥ 40% and an ECOG performance status of 0–2. This response requirement reflects institutional practice during earlier treatment eras and does not represent a universal standard of care.

The decision to proceed with allogeneic transplantation was based on institutional policy and physician discretion, particularly during the period between 2010 and 2013 when allo-SCT was more actively pursued. Candidates were typically younger patients (≤ 55 years) with high-risk clinical features.

According to institutional practice, tandem transplantation was not routinely performed. The vast majority of patients underwent a single transplant. A second transplant was considered only in selected cases of disease relapse after the first transplant.

The decision to proceed with allogeneic transplantation was based on institutional policy and physician discretion, particularly during the period between 2010 and 2013 when allo-SCT was more actively pursued. Candidates were typically younger patients (≤ 55 years) with high-risk clinical features.

According to institutional practice, tandem transplantation was not routinely performed. The vast majority of patients underwent a single transplant. A second transplant was considered only in selected cases of disease relapse after the first transplant. Allogeneic transplantation following prior autologous transplant was reserved for patients who fulfilled institutional eligibility criteria, including younger age and features suggestive of higher-risk disease.

Peripheral blood stem cells for ASCT were mobilized using granulocyte colony-stimulating factor (G-CSF) at 16 µg/kg for five days, without chemotherapy-based priming. The conditioning regimen consisted of melphalan 200 mg/m², which was reduced to 140 mg/m² for patients with renal impairment (creatinine clearance < 30 mL/min) or age above 60 years.

For allogeneic transplantation (allo-SCT), the donor stem cells were collected via apheresis following G-CSF mobilization and infused fresh. The conditioning regimen consisted of fludarabine (30 mg/m² daily from day − 5 to -1) and melphalan (140 mg/m² on day − 1) representing a reduced-intensity conditioning (RIC) approach.

Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine and methotrexate according to standard protocols. All patients received standard antimicrobial prophylaxis, including acyclovir for herpes simplex virus, fluconazole for fungal infections, and trimethoprim-sulfamethoxazole for Pneumocystis jirovecii , as described previously [ 12 , 13 ].

Maintenance therapy following ASCT was not uniformly implemented throughout the study period. However, in more recent years (post-2015), a subset of patients received IMiD-based maintenance, predominantly lenalidomide, in accordance with emerging evidence and international guidelines demonstrating improved progression-free and overall survival [ 6 , 8 ]. Due to inconsistent documentation, maintenance therapy was not included in comparative outcome analyses.

Response and engraftment monitoring

We applied standard International Myeloma Working Group criteria to define treatment responses, including complete response (CR) and very good partial response (VGPR). Disease relapse or progression was also defined according to these consensus criteria. For patients undergoing allo-SCT, donor chimerism was assessed on days + 30, +90, + 180, and + 365 post-transplant. Patients who relapsed after allo-SCT were eligible for donor lymphocyte infusion in the absence of active GVHD. The diagnosis and grading of acute and chronic GVHD were performed using established clinical criteria [ 14 , 15 ].

Statistical analysis

The primary endpoints of this study were overall survival (OS) and Progression-Free Survival (PFS). Secondary endpoints included non-relapse mortality (NRM) and cumulative incidence of relapse. We compared baseline characteristics between the ASCT and allo-SCT groups using the Mann-Whitney U test for continuous variables and the chi-square test for categorical variables.

Survival probabilities were estimated using the Kaplan-Meier method and compared with the log-rank test. Multivariable or propensity score–adjusted analyses were not performed due to missing baseline variables and treatment heterogeneity across eras. Given the substantial missingness and heterogeneity, multivariable modeling was considered unreliable and therefore not performed.

The cumulative incidence of relapse and NRM were calculated to account for competing risks and compared using the Fine and Gray test. All statistical analyses were performed with SPSS software (version 26.0, IBM) and R software (version 2.1.0) with the ‘cmprsk’ package. A two-sided p -value of less than 0.05 was considered statistically significant.

Results

Patient demographics and transplant characteristics

Our analysis included 1,342 patients with multiple myeloma, of whom 1,226 (91.4%) underwent autologous transplantation (ASCT) and 116 (8.6%) received an allogeneic transplant (allo-SCT) from an HLA-identical sibling donor. A second transplant was performed in a small proportion of patients. In the ASCT group, 23 patients (1.9%) underwent a second transplant, compared to 19 patients (16.4%) in the allo-SCT group. Overall, 42 patients (3.1%) in the entire cohort received a second transplant. These findings indicate that the vast majority of patients underwent a single transplant, consistent with institutional practice, with repeat transplantation reserved for selected cases of disease relapse.

The median time from diagnosis to transplantation was 13.6 months (range: 4.6–177.0). Patients undergoing allo-SCT had a longer median interval compared to those receiving ASCT (17.9 vs. 13.4 months), potentially reflecting differences in patient selection and treatment strategy. The cohort had a substantial median follow-up of 101 months (range, 1-338).

Reflecting the more stringent eligibility criteria for allo-SCT, patients in this group were significantly younger than those in the ASCT group (median age 47 vs. 55 years). A male predominance was observed across the entire cohort (62.1%) and was consistent between both treatment arms. The baseline characteristics of the patients are detailed in Table 1 . Cytogenetic and molecular risk stratification was unavailable for a substantial proportion of patients and therefore not included in comparative analyses.

Baseline laboratory characteristics at diagnosis, stratified by transplant modality and clinical outcomes, are presented in Table 2 . In univariate analysis, elevated LDH ( p < 0.001), low hemoglobin ( p = 0.00001), and hypoalbuminemia ( p = 0.0002) were significantly associated with relapse. In contrast, only hypoalbuminemia was significantly associated with non-relapse mortality ( p = 0.006), while LDH ( p = 0.13) and creatinine ( p = 0.31) were not.

Among these variables, LDH showed the strongest association with relapse, whereas albumin was the only parameter associated with both relapse and NRM. These findings suggest that baseline laboratory markers reflect distinct biological dimensions, with LDH capturing disease aggressiveness and albumin reflecting patient frailty and physiologic reserve.

Survival outcomes

When we analyzed long-term survival, we found a clear divergence between disease control and overall survival. Landmark analysis showed no significant difference in overall survival (OS) between the two strategies ( p = 0.38, Fig. 1 ), despite marked differences in relapse incidence and non-relapse mortality. The 5-year OS was 74.7% for ASCT recipients and 70.6% for allogeneic recipients, with these rates evolving to 59.2% and 64.0%, respectively, at the 10-year mark (Table 3 ). Fig. 1 Overall Survival (OS) according to transplant type. Kaplan–Meier curves depicting overall survival following autologous and allogeneic transplantation. No significant OS difference was observed between the two modalities ( p = 0.38)

In contrast, Progression-Free Survival (PFS) was significantly superior in the allogeneic cohort ( p = 0.002, Fig. 2 ). The benefit was evident early and persisted long-term. At 5 years, PFS was 60.8% after allo-SCT compared to 42.9% after ASCT. By 10 years, this advantage was maintained, with PFS rates of 50.6% and 26.0%, respectively. Fig. 2 Progression-free survival (PFS) according to transplant type. Kaplan–Meier analysis showing significantly improved PFS in the allogeneic transplant group compared to autologous recipients ( p = 0.002)

Relapse and treatment-related mortality

The superior disease control with allo-SCT was directly reflected in the relapse incidence. The risk of relapse was significantly higher following ASCT ( p < 0.001, Fig. 3 ), with a cumulative incidence that climbed steadily to 68.7% at 10 years. Conversely, the allogeneic group experienced a markedly lower and more stable relapse risk, with a 10-year incidence of 32.5%. Fig. 3 Cumulative incidence of relapse after transplantation. Comparison of relapse incidence using cumulative incidence analysis. Allo-SCT was associated with a markedly lower 10-year relapse rate (32.5% vs. 68.7%; p < 0.001)

This reduction in relapse was offset by a substantially increased risk of non-relapse mortality. As anticipated, non-relapse mortality (NRM) was substantially higher in the allogeneic group ( p < 0.001, Fig. 4 ), primarily driven by transplant-related complications. The 5-year NRM was 20.4% for allo-SCT recipients versus 8.0% for ASCT recipients, a difference that remained apparent at 10 years (23.4% vs. 12.9%). Fig. 4 Cumulative Incidence of Non-Relapse Mortality (NRM). Cumulative incidence plots for non-relapse mortality demonstrating higher treatment-related mortality after allogeneic transplantation (10-year NRM: 23.4% vs. 12.9%; p < 0.001)

Graft-versus-host disease

The major complication of allo-SCT, graft-versus-host disease (GVHD), was observed at expected rates. The cumulative incidence of acute and chronic graft-versus-host disease (GVHD) was assessed exclusively following allo-HSCT. The cumulative incidence of grade 2–4 acute GVHD at 90 days was 24.8% (95% CI: 15.4% to 38.6%).

The cumulative incidence of extensive chronic GVHD increased over time. At 1-year post-transplant, the incidence was 25.9% (95% CI: 18.5% to 35.5%). This incidence continued to rise, reaching 32.2% (95% CI: 24.1% to 42.3%) at 3 years and 35.4% (95% CI: 26.6% to 46.0%) at 5 years. Chronic GVHD likely contributed to late morbidity and impaired quality of life, although formal quality-of-life assessments were not performed.

Discussion

This large, long-term single-center study provides a nuanced comparison of autologous and allogeneic transplantation in multiple myeloma, highlighting a classic therapeutic trade-off. The low rate of second transplantation in our cohort reflects a non-tandem strategy, with repeat transplantation reserved for relapse rather than planned sequential therapy. This approach differs from tandem auto-allo strategies evaluated in clinical trials and should be considered when interpreting outcomes.

Our data confirm the potent graft-versus-myeloma effect associated with allo-SCT, which translated into a significantly superior PFS and a markedly lower cumulative incidence of relapse compared to ASCT. However, this superior disease control was precisely counterbalanced by a significantly higher risk of non-relapse mortality, resulting in no detectable difference in long-term overall survival between the two strategies.

These findings support a biologically plausible distinction between relapse and non-relapse mortality: relapse appears to be driven primarily by disease related factors such as proliferative activity (reflected by LDH), whereas non-relapse mortality is more closely associated with host-related vulnerability, as captured by hypoalbuminemia.

Our findings reveal a significantly lower relapse rate in the allo-HSCT group compared to ASCT (32.5% versus 68.7% at 10 years), consistent with the well-established graft-versus-myeloma effect observed in randomized trials and retrospective series [ 16 , 17 ]. These findings resonate with the historical challenge in the field: how to harness the curative potential of the allogeneic immune system without incurring its prohibitive toxicity.

Our results are consistent with earlier randomized trials, meta-analyses, and more recent registry-based studies demonstrating that although allo-SCT reduces relapse risk, this benefit is often offset by increased non-relapse mortality, limiting its impact on overall survival [ 16 – 20 ]. A contemporary review and registry-based analysis further support the view that allo-SCT may provide durable disease control in selected patients, but its broader application remains constrained by toxicity and competing modern therapeutic options [ 19 , 20 ].

These findings reflect and extend the conclusions of systematic reviews and long-term follow-ups, which suggest that allo-HSCT does not provide clear survival benefit in standard-risk MM but may neutralize adverse cytogenetics in selected high-risk patients [ 21 , 22 ]. Notably, the incidence of acute and chronic GVHD in our allo-HSCT cohort (16.5% and 31.3%, respectively) mirrors large international transplant registries, where GVHD remains a major contributor to late morbidity and mortality [ 18 , 22 ]. Our real-world NRM rates, although high, underline the continued challenges of allogeneic transplantation in clinical practice, even with improved supportive care and patient selection.

The standard of care for transplant-eligible patients remains ASCT, as confirmed in our data and multiple large studies. When combined with novel induction regimens, ASCT provides robust long-term survival and a favorable risk–benefit profile [ 8 , 17 ]. Indeed, current guidelines and recent phase III trials support upfront ASCT for newly diagnosed MM, and its role is reinforced by the sustained improvement in progression-free and overall survival [ 8 ].

The declining use of allo-SCT over the past decade is therefore understandable, accelerated by the arrival of highly active novel immunotherapies. While CAR-T cell therapies and bispecific antibodies achieve deep remissions, their long-term curative potential remains uncertain, particularly in high-risk disease [ 11 ]. In the current treatment landscape, our findings suggest that the niche for allo-SCT is increasingly narrow. It may be considered in selected young patients with ultra-high-risk disease biology or those with early relapse after modern ASCT-based regimens, and ideally within the context of clinical trials. The integration of measurable residual disease (MRD) assessment, alongside precise risk stratification, can further aid in selecting suitable candidates for transplantation and optimizing post-transplant strategies [ 8 ]. Future approaches should focus on strategies to mitigate the toxicity of allo-SCT, perhaps through better graft engineering, refined conditioning regimens, or improved post-transplant supportive care.

It is important to consider the limitations of our study when interpreting these results including its retrospective design, strong selection bias, lack of uniform cytogenetic and MRD assessment, absence of multivariable adjustment, and substantial treatment heterogeneity across eras. As a large, retrospective analysis conducted in a resource-limited setting, we were unable to perform uniform risk stratification, such as cytogenetic analysis or FISH, for all patients. Furthermore, minimal residual disease (MRD) assessment was not routinely available during most of the study period. The absence of this data prevents us from determining whether the benefits of allo-SCT might be more pronounced in specific molecular subgroups, such as those with high-risk genetics. Nevertheless, the strengths of our study lie in its large sample size and exceptionally long follow-up, which provide robust, real-world insights into the long-term trajectories of these two transplant strategies. Our experience thus reflects the practical challenges and outcomes in a setting where advanced diagnostics are still becoming widely accessible.

Conclusion

In conclusion, our long-term experience delineates the divergent outcomes of these two transplant modalities. Allo-SCT offers a powerful graft-versus-myeloma effect capable of durable disease control in a minority of carefully selected patients. Yet, for the majority of patients, this advantage is nullified by the procedure’s inherent risks. Autologous transplantation therefore remains the standard of care, providing an excellent balance of efficacy and safety. The future of myeloma therapy will likely involve further personalization, where the decision to pursue an allogeneic approach is guided by minimal residual disease status, refined risk stratification, and the careful integration of novel immune-based strategies to maximize survival while preserving quality of life and minimizing long-term treatment-related mortality.

Table 1 Baseline demographic and clinical characteristics of patients and donors Characteristic Total ( N = 1342) Autologous ( N = 1226) Allogeneic ( N = 116) Patient Gender, n (%) Male 833 (62.1) 766 (62.5) 67 (57.8) Female 509 (37.9) 460 (37.5) 49 (42.2) Donor Gender, n (%) Male - - 68 (58.6) Female - - 48 (41.4) Patient Age, years Median 54 55 47 Range 21–71 25–71 21–56 Donor Age, years Median - - 46 Range - - 22–75 This table summarizes the key demographic and transplant-related characteristics of the study population, including patient age, sex distribution, and donor profiles across the autologous (ASCT) and allogeneic (allo-SCT) transplantation cohorts. Continuous variables are expressed as medians (range) and categorical variables as numbers (percentages)

Table 2 Baseline laboratory characteristics at diagnosis stratified by transplant type and clinical outcomes Outcome Hb < 10 g/dL LDH > ULN Cr ≥ 2 mg/dL Alb < 3.5 g/dL Autologous SCT NRM 40 (71.4%) 10 (22.7%) 20 (35.7%) 28 (56.0%) Relapse 264 (72.9%) 94 (39.2%) 103 (31.1%) 134 (53.8%) Censored 328 (58.9%) 113 (17.8%) 184 (28.2%) 259 (41.4%) Total 632 (64.8%) 217 (23.6%) 307 (29.5%) 421 (45.5%) Allogeneic SCT NRM 12 (66.7%) 6 (33.3%) 6 (27.3%) 12 (66.7%) Relapse 16 (76.2%) 14 (60.9%) 6 (28.6%) 13 (59.1%) Censored 34 (61.8%) 8 (11.6%) 10 (16.9%) 25 (35.2%) Total 62 (66.0%) 28 (25.5%) 22 (21.6%) 50 (45.0%) Overall Cohort NRM 52 (70.3%) 16 (25.8%) 26 (33.3%) 40 (58.8%) Relapse 280 (73.1%) 108 (41.1%) 109 (31.0%) 147 (54.2%) Censored 362 (59.2%) 121 (17.2%) 194 (27.3%) 284 (40.7%) Total 694 (64.9%) 245 (23.8%) 329 (28.8%) 471 (45.5%) Data are presented as number (percentage). Percentages were calculated within each outcome group. LDH lactate dehydrogenase, ULN upper limit of normal, Cr creatinine, Alb albumin, NRM non-relapse mortality

Table 3 Comparison of long-term outcomes between autologous and allogeneic stem cell transplantation in multiple myeloma Outcome Time (months) ASCT (95% CI) Allogeneic (95% CI) P -value Overall Survival 60 74.7% (71.0–78.0) 70.6% (60.7–78.5) 0.38 120 59.2% (53.1–64.8) 64.0% (52.1–73.7) Disease-Free Survival 60 42.9% (38.7–46.1) 60.8% (50.6–69.5) 0.002 120 26.0% (21.3–30.9) 50.6% (35.1–64.3) Relapse Incidence 60 52.9% (48.9–56.9) 22.3% (14.9–32.2) < 0.001 120 68.7% (63.4–73.9) 32.5% (18.4–53.4) NRM Incidence 60 8.0% (6.1–10.6) 20.4% (13.7–29.8) < 0.001 120 12.9% (9.0–18.2) 23.4% (15.3–34.8) This table presents survival outcomes and cumulative incidence rates for overall survival (OS), disease-free survival (DFS), relapse, and non-relapse mortality (NRM) at 5- and 10-years post-transplant. Values are expressed as percentages with 95% confidence intervals (CI). P -values were calculated using the log-rank and Fine–Gray tests as appropriate

The original version of this article was revised: This article was originally published with the first author’s name was incorrectly published and should be corrected to “Sahar Tavakkoli Shiraji”. In addition, the name “Maryam Barkhordar” was inadvertently duplicated; the second occurrence should be removed, with the correct listing retaining her position as the third author.

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Change history

5/11/2026

A Correction to this paper has been published: 10.1007/s00277-026-07065-2

Author contributions

S.T.S. and M.B. designed the study, collected the data, and wrote the main manuscript text. M.Ba. performed the statistical analysis and prepared the tables and figures. S.R., G.S., H.K.F., D.B., M.Y., and S.A.M., contributed to data collection and patient follow-up. G.J., K.A., M.Ba. and M.V. supervised the study and critically revised the manuscript. A.G. provided the main idea of the study. All authors reviewed and approved the final manuscript.

Funding

This research received no external funding.

Data availability

The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Conducted according to the Declaration of Helsinki. Ethics approval was waived due to retrospective anonymized design.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

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