Abstract
Background: We performed a systematic review and meta-analysis to compare the clinical outcomes and toxicity of reduced-intensity conditioning (RIC) and myeloablative conditioning (MAC) allogeneic hematopoietic stem cell transplantation (alloHSCT) in patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Evidence acquisition: A comprehensive PubMed and Embase search was performed using the following keywords: “reduced-intensity”, “myeloablative”, “AML”, and “MDS”. The primary endpoints were overall survival (OS) and event-free survival (EFS), and the secondary endpoints were relapse incidence (RI), non-relapse mortality (NRM), grade II-IV acute graft-versus-host disease (aGVHD), and chronic GVHD (cGVHD). Results: Eight studies (2 prospective and 6 retrospective) involving 6464 patients who received RIC (n = 1571) or MAC (n = 4893) alloHSCT were included in the analysis. Median age and the number of patients with low hematopoietic cell transplantation-specific comorbidity index scores and who received ex vivo or in vivo T cell depletion were higher in the RIC arm than in the MAC arm. Significant heterogeneity was not found among the studies for any of the endpoints except for grade II-IV aGVHD. OS (odds ratio [OR], 0.96; 95% confidence interval [CI], 0.84-1.08; p = 0.47) and EFS (OR, 0.88; 95% CI, 0.77-1.00; p = 0.05) were similar in the RIC and MAC arms, whereas RI (OR, 1.41; 95% CI, 1.24-1.59; p < 0.00001) was higher in the RIC arm than in the MAC arm. The incidence of grade II-IV aGVHD (OR, 0.59; 95% CI, 0.36-0.96; p = 0.03) was lower in the RIC arm than in the MAC arm; however, NRM (OR, 0.99; 95% CI, 0.87-1.13; p = 0.85), total cGVHD (OR, 1.10; 95% CI, 0.88-1.38; p = 0.38), and extensive cGVHD (OR, 1.01; 95% CI, 0.75-1.37; p = 0.95) were not significantly different between the two arms. Conclusion: RIC alloHSCT may be an effective treatment strategy for AML/MDS patients who are not suitable candidates for MAC alloHSCT. However, heterogeneity in baseline patient characteristics and treatment protocols may have influenced the outcomes of RIC alloHSCT in our analysis. Future randomized controlled trials are needed to confirm our findings.
Keywords: Reduced-intensity conditioning, myeloablative conditioning, allogeneic hematopoietic stem cell transplantation, acute myeloid leukemia, myelodysplastic syndrome, meta-analysis, systematic review
Introduction
Currently, allogeneic hematopoietic stem cell transplantation (alloHSCT) is the only potentially curative approach for acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS) treatment [1,2]. However, procedure-related toxicities restrict the use of myeloablative conditioning (MAC) alloHSCT to AML patients younger than 50 years with a good performance status and who are usually in first complete remission (CR1). Reduced-intensity conditioning (RIC) alloHSCT has been shown to reduce procedure-related toxicities with acceptable relapse incidence (RI). Thus, RIC has extended the application of alloHSCT in AML/MDS to include patients who are not eligible candidates for standard alloHSCT because of advanced age or comorbidities [3-6]. Furthermore, RIC alloHSCT can provide adequate immunosuppression and allow successful donor hematopoietic engraftment to eradicate malignant clonal cells through a graft versus malignancy effect, independent of chemoradiotherapy [7,8].
Despite the wide use of RIC alloHSCT for the treatment of AML/MDS, few randomized clinical trials have compared the clinical outcomes between RIC and MAC alloHSCT in AML/MDS. Furthermore, retrospective studies comparing the clinical outcomes of RIC and MAC alloHSCT in AML/MDS patients have produced conflicting results. Therefore, we performed a comprehensive systematic review and meta-analysis to compare the clinical outcomes and toxicity of RIC and MAC alloHSCT in patients with AML/MDS.
Materials and methods
Data sources
PubMed and Embase were searched for English-language articles published between January 1995 and May 2014. The National Institutes of Health Clinical Trials Registry (http://clinicaltrials.gov/) and Current Controlled Trials in the metaRegister of Controlled Trials (http://www.controlled-trials.com/) were also searched for related articles. Online abstracts from the following annual meetings were also reviewed: American Society of Hematology, European Hematology Association, Center for International Blood & Marrow Transplant Research (CIBMTR), European Society for Blood and Marrow Transplantation (EBMT), and American Society for Blood and Marrow Transplantation. Keywords used in the search were “reduced-intensity”, “myeloablative conditioning”, “AML”, and “MDS”. Eligible studies included clinical trials comparing RIC alloHSCT and MAC alloHSCT in adult AML or MDS patients (16 years or older). Clinical trials involving AML patients with relapsed, refractory, or advanced disease, MDS patients with progressive disease, or subjects undergoing umbilical cord blood transplantation were ineligible for analysis. Studies comparing the outcomes between non-myeloablative (NMA) conditioning and MAC regimens were also ineligible for analysis. RIC was defined as follows [9-11]: (1) ≤ 500 Gy for single-fraction total body irradiation (TBI) or ≤ 800 Gy for fractionated TBI; (2) ≤ 9 mg/kg oral or intravenous busulfan; (3) ≤ 140 mg/m2 melphalan; (4) < 10 mg/kg thiotepa; or (5) BEAM (carmustine, etoposide, cytarabine, and melphalan) pretreatment. NMA was defined as follows: (1) 200-Gy fractionated TBI; (2) TBI (200 Gy) plus fludarabine (Flu); or (3) Flu plus cyclophosphamide [8,12-14].
Study selection
Published articles were carefully screened, and only the most current articles with the longest follow-ups were included in the analysis in cases of overlapping information between publications. Preclinical studies, case reports, and reviews were excluded from the analysis.
Clinical endpoints
Study data including patient characteristics, treatment protocol, endpoint definitions, results, and follow-up information were extracted by two independent reviewers (ZW and HLF). In cases of discrepancies between the reviewers, the data were re-extracted until a consensus was reached. The primary endpoints of the analysis were overall survival (OS) and event-free survival (EFS), and the secondary endpoints were RI, non-relapse mortality (NRM), grade II-IV acute graft-versus-host disease (aGVHD), and chronic GVHD (cGVHD). OS was defined as the time from transplantation to the time of death from any cause or last follow-up. EFS was defined as the time from transplantation to the time of relapse or death from any cause. NRM was defined as the incidence of death not related to relapse.
Statistical analyses
Statistical analyses were performed using RevMan 5.0 software. Publication bias was calculated using Comprehensive Meta-Analysis (Biostat, Englewood, NJ, USA) and analyzed using Begg’s and Egger’s tests. Data regarding OS, RI, NRM, EFS, grade II-IV aGVHD, and cGVHD were directly extracted from the studies. Two-tailed P values < 0.05 were considered statistically significant. Before the meta-analysis, Cochrane’s Q and I2 statistics were used to evaluate heterogeneity among the studies. The random effects model was used to calculate pooled effects.
Results
Study characteristics
Eight studies involving 6464 AML/MDS patients were included in the analysis [12,14-20]. Of the 6464 AML/MDS patients, 1571 patients received RIC alloHSCT and 4893 patients received MAC alloHSCT. Patient and treatment characteristics and clinical outcomes of the eligible studies are listed in Tables 1, 2, 3 and 4, respectively.
Table 1.
Characteristics of the eligible trials included in the meta-analysis
| Reference | Disease | Study type | Centers |
|---|---|---|---|
| Bornh��user 2012 [15] | AML | prospective | multicenters |
| Hiramoto 2014 [16] | MDS/AML-MLD | retrospective | single |
| Khabori 2011 [17] | AML/MDS | retrospective | single |
| Lioure 2012 [18] | AML | prospective | multicenters |
| Luger 2012 [14] | AML/MDS | retrospective | multicenters |
| Martino 2012 [12] | AML/MDS | retrospective | multicenters |
| Philipp 2010 [19] | AML | retrospective | single |
| Shimoni 2012 [20] | AML/MDS | retrospective | single |
Note: AML, acute myeloid leukemia; AML-MLD: acute myeloid leukemia with multilineage dysplasia; MDS myelodysplastic syndrome.
Table 2.
Patient’s characteristics of the eligible trials included in the meta-analysis
| Reference | Conditioning regimen | No. of pts | Meidan Age at HCT (range) | Male, no. (%) | Cytogenetic risk, unfavorable/poor, no. (%) | Karnofsky score at HCT, no. (%) | HCT-CI score, ≥ 3 (high), no. (%) | Disease status at HCT, no. (%) | BM blast < 5% at HCT, no. (%) | MRD, no. (%) | MUD, no. (%) | Donor Related, no. (%) | HLA match, no. (%) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Bornhäuser 2012 [15] | RIC | 99 | 44 (18-60) | 43 (43) | 22 (22) | NA | 15 (15) | CR1, 99 (100) | 99 (100) | 59 (60) | 28 (28) | 59 (60) | 87 (88) |
| MAC | 96 | 45 (18-60) | 47 (49) | 26 (27) | NA | 17 (18) | CR1, 96 (100) | 96 (100) | 58 (60) | 24 (25) | 58 (60) | 82 (85) | |
| Hiramoto 2014 [16] | RIC | 81 | 57 (19-68) | 58 (72) | 33 (41) | < 90%, 14 (17) | NA | CR, 42 (52) | 42 (52) | NA | NA | 43 (53) | 70 (86) |
| MAC | 34 | 46 (23-57) | 24 (71) | 7 (21) | < 90%, 5 (15) | NA | CR, 18 (53) | 18 (53) | NA | NA | 12 (35) | 31 (91) | |
| Khabori 2011 [17] | RIC | 39 | 53 (42-60) | 19 (49) | NA | median, 90% | 11 (28) | CR, 39 (100) | 39 (100) | NA | NA | 18 (46) | NA |
| MAC | 62 | 50 (40-59) | 32 (52) | NA | median, 90% | 7 (11) | CR, 62 (100) | 62 (100) | NA | NA | 42 (68) | NA | |
| Lioure 2012 [18] | RIC | 47 | 54 (34-60) | 17 (36) | 10 (21) | NA | NA | CR, 47 (100) | 47 (100) | 47 (100) | 0 | 47 (100) | 47 (100) |
| MAC | 117 | 39 (17-50) | 67 (57) | 14 (12) | NA | NA | CR, 117 (100) | 117 (100) | 115 (98) | 0 | 117 (100) | 115 (98) | |
| Luger 2012 [14] | RIC | 1041 | 55 (18-70) | 604 (58) | 227 (22) | < 90%, 322 (31) | NA | CR, 408 (39); MDS untreated 123 (40) | 770 (74) | 376 (36) | 307 (29) | 376 (36) | 683 (66) |
| MAC | 3731 | 42 (18-68) | 1991 (53) | 691 (17) | < 90%, 1190 (32) | NA | CR, 1754 (47); MDS untreated, 110 (12) | 2842 (76) | 1560 (42) | 999 (27) | 1560 (42) | 2559 (69) | |
| Martino 2012 [12] | RIC | 126 | 54 (19-70) | 64 (51) | 14 (21) | < 80%, 5 (4) | NA | CR+PR, 126 (100) | < 10%, 126 (100) | 126 (100) | NA | 126 (100) | 126 (100) |
| MAC | 718 | 39 (18-63) | 367 (51) | 86 (12) | < 80%, 17 (2.4) | NA | CR+PR, 718 (100) | < 10%, 718 (100) | 718 (100) | NA | 718 (100) | 718 (100) | |
| Philipp 2010 [19] | RIC | 37 | 51 (19-68) | 15 (41) | 13 (35) | NA | 18 (49) | CR1, 37(100) | 37 (100) | 22 (60) | 13 (35) | 22 (60) | 35 (95) |
| MAC | 56 | 34 (17-66) | 24 (43) | 15 (27) | NA | 7 (13) | CR1, 56 (100) | 56 (100) | 37 (66) | 16 (29) | 37 (66) | 53 (95) | |
| Shimoni 2012 [20] | RIC | 106 | 60 (29-75) | 61 (58) | 26 (29) for AML | NA | 28 (26) | CR1 or MDS with BM Blast < 10%, 54 (51) | NA | 47 (44) | 55 (52) | 47 (44) | 55 (52) |
| MAC | 85 | 49 (18-66) | 48 (56) | 13 (19) for AML | NA | 10 (12) | CR1 or MDS with BM Blast < 10%, 34 (40) | NA | 42 (49) | 41 (48) | 42 (49) | 41 (48) |
Note: BM, bone marrow; CR, complete remission; HCT, hematopoietic cell transplantation; HCT-CI, hematopoietic cell transplantation-specific comorbidity index; HLA, human leukocyte antigen; MAC, myeloablative conditioning; MRD, human leukocyte antigen-identical sibling; MUD, matched unrelated donor; NA, not available; PR, partial remission; RIC, reduced-intensity conditioning.
Table 3.
Treatment characteristics of the eligible trials included in the meta-analysis
| MAC | 62 | 54 (87) | Ale, in unrelated donor transplants, 20 (32) | Ref [17]* | CsA/MMF or CsA/MTX in related donor HCT, Ale/CsA in unrelated donor HCT | |
|---|---|---|---|---|---|---|
| Lioure 2012 [18] | RIC | 47 | 47 (100) | ATG, 47 (100) | Orally 4 mg/kg Bu daily for 2 d plus 30 mg/m² Flu daily for 4 d (100) | CSA (100) |
| MAC | 117 | 0 | None | Six dose of 2 Gy TBI for 3 d plus 60 mg/kg CY daily for 2 d (100) | CSA + MTX (100) | |
| Luger 2012 [14] | RIC | 1041 | 768 (74) | ATG, 438 (30) | Ref [14]* | CNI + MTX ± other (44), CNI ± other (56) |
| MAC | 3731 | 1720 (46) | ATG, 631 (17) | Ref [14]* | CNI + MTX ± other (88), CNI ± other (12) | |
| Martino 2012 [12] | RIC | 126 | 115 (91) | Ex vivo TCD, 2 (2); Ale, 12 (9); ATG, 42 (33) | Ref [12]* | CsA, CsA/MTX, CsA/others |
| MAC | 718 | 465 (65) | Ex vivo TCD, 130 (18); Ale, 52 (7.2); ATG, 36 (5) | Ref [12]* | CsA, CsA/MTX, CsA/others | |
| Philipp 2010 [19] | RIC | 37 | 36 (97.3) | ATG, 37 (100) | Orally 4 mg/kg Bu daily for 2 d plus 30 mg/m² Flu daily for 6 d (100) | CsA/MMF (100) |
| MAC | 56 | 47 (83.9) | ATG, 3 (5.4) | Six dose of 2 Gy TBI for 3 d plus 60 mg/kg CY daily for 2 d (100) | CsA/MTX (100) | |
| Shimoni 2012 [20] | RIC | 106 | NA | ATG, in unrelated or mismatched donor and patients with no prior chemotherapy | I.v. 3.2 mg/kg Bu daily for 2 d plus 30 mg/m² Flu daily for 5 d (100) | CsA/MTX (100) |
| MAC | 85 | NA | ATG, in unrelated or mismatched donor and patients with no prior chemotherapy | I.v. 3.2 mg/kg Bu daily for 4 d plus 40 mg/m² Flu daily for 4 d (100) | CsA/MTX (100) |
multiple regimens are used in this study with details in the reference;
2-CdA, cladribine; Ale, Alemtuzumab; ATG, antithymocyte globulin; Bu, busulfan; CNI, calcineurin inhibitor; CsA, cyclosporine; CY, cyclophosphamide; Flu, fludarabine; GVHD, graft-versus-host disease; HCT, hematopoietic cell transplantation; MAC, myeloablative conditioning; MMF, mycophenolate mofetil; MTX, methotrexate; PBSC, peripheral blood stem cells; RIC, reduced-intensity conditioning; TBI, total body irradiation; TCD, T cell depletion.
Table 4.
Transplantation outcomes of the eligible trials included in the meta-analysis
| Reference | Conditioning regimen | No. of pts | Median follow-up in survivors, months (range) | Grade II-IV aGVHD, no. (%) | Extensive cGVHD, no. (%) | Total cGVHD, no. (%) | OS, % | EFS, % | NRM, % | RI, % |
|---|---|---|---|---|---|---|---|---|---|---|
| Bornhäuser 2012 [15] | RIC | 94 | 27 (4-81) | 17 (17) | 22 (22) | NA | 3-yr, 61 | 3-yr, 58 | 3-yr, 13 | 3-yr, 28 |
| MAC | 90 | 27 (4-81) | 23 (24) | 16 (17) | NA | 3-yr, 58 | 3-yr, 56 | 3-yr, 18 | 3-yr, 26 | |
| Hiramoto 2014 [16] | RIC | 81 | 47 (4-125) | 36 (44) | 37 (50) | 43 (58) | 4-yr, 42 | NA | 4-yr, 33 | 4-y, 25 |
| MAC | 34 | 40 (4-130) | 12 (35) | 11 (39) | 15 (53) | 4-yr, 47 | NA | 4-yr, 29 | 4-y, 26 | |
| Khabori 2011 [17] | RIC | 39 | 34.3 (3.3-76.4) | 24 (62) | 18 (46) | 22 (56) | 3-yr, 50 | 3-yr, 45 | 3-yr, 25 | 3-yr, 31 |
| MAC | 62 | 34.3 (3.3-76.4) | 40 (65) | 37 (60) | 40 (65) | 3-yr, 49 | 3-yr, 47 | 3-yr, 31 | 3-yr, 22 | |
| Lioure 2012 [18] | RIC | 47 | 88 (16-119) | 5 (11) | 5 (11) | 16 (34) | 5-yr, 70; 9-yr, 69 | 9-yr, 66 | 3-yr, 4.2; 5-yr, 4.4; 9-yr, 6.5 | 3-yr, 21; 5-yr, 28; 9-yr, 29 |
| MAC | 117 | 88 (30-119) | 61 (52) | 20 (17) | 34 (29) | 5-yr, 70; 9-yr, 68 | 9-yr, 63 | 3-yr, 13; 5-yr, 13; 9-yr, 16 | 3-yr, 19; 5-yr, 19; 9-yr, 22 | |
| Luger 2012 [14] | RIC | 1041 | 41 (3-124) | 451 (44) | NA | 427 (42) | 5-yr, 33 | 5-yr, 30 | 5-yr, 35 | 5-yr, 40 |
| MAC | 3731 | 58 (3-128) | 1720 (49) | NA | 1466 (40) | 5-yr, 34 | 5-yr, 33 | 5-yr, 34 | 5-yr, 32 | |
| Martino 2012 [12] | RIC | 126 | 76 (42-135) | NA | 32 (25) | 65 (52) | 7-yr, 53 | 7-yr, 48* | 7-yr, 18 | 7-yr, 34 |
| MAC | 718 | 82 (27-149) | NA | 184 (26) | 312 (44) | 7-yr, 56 | 7-yr, 54* | 7-yr, 23 | 7-yr, 23 | |
| Philipp 2010 [19] | RIC | 37 | NA | 6 (16) | 15 (41) | 21 (57) | 5-yr, 61 | 5-yr, 53 | 5-yr, 16 | 5-yr, 36 |
| MAC | 56 | NA | 24 (43) | 22 (39) | 25 (45) | 5-yr, 56 | 5-yr, 54 | 5-yr, 20 | 5-yr, 32 | |
| Shimoni 2012 [20] | RIC | 106 | 48 (1-122)# | 27 (25) | NA | 50 (47) | 5-yr, 44 | NA | 5-yr, 20 | 5-yr, 47 |
| MAC | 85 | 29 (4-89)# | 31 (37) | NA | 51 (60) | 5-yr, 50 | NA | 5-yr, 18 | 5-yr, 40 |
progression-free survival instead of EFS is evaluated in this study;
the median follow-up time is for all patients instead of survivors in this study;
aGVHD, acute graft-versus-host disease; cGVHD, chronic graft-versus-host disease; EFS, event-free survival; MAC, myeloablative conditioning; NA, not available; NRM, non-relapse mortality; OS, overall survival; RI, relapse incidence; RIC, reduced-intensity conditioning; yr, year.
The distribution of baseline patient characteristics was heterogeneous. Factors contributing to the baseline heterogeneity included median age, hematopoietic cell transplantation-specific comorbidity index (HCT-CI) score, and the bone marrow (BM) blast count at HSCT. Median age was significantly higher in the RIC arm than in the MAC arm, with over half of the patients in the RIC arm being over 51 years of age. Four studies [15,17,19,20] evaluated HCT-CI scores. The proportion of patients with low HCT-CI scores was greater in the RIC arm than in the MAC-HSCT arm (25.6% [72/281] vs. 13.7% [41/299]; p = 0.04). The proportion of patients with < 5% BM blasts at alloHSCT was 77% (1034/1344) in the RIC arm and 79% (3191/4024) in the MAC arm (p = 0.01). Twenty-two percent (345/1537) of patients in the RIC arm and 18% (852/4837) of patients in the MAC arm had unfavorable/high-risk cytogenetics (p = 0.05). The Karnofsky score at alloHSCT was not significantly different between the RIC and MAC arms (p = 0.70).
Thirty-seven percent (677/1816) and 31% (403/1283) of patients in the RIC arm and 53% (2530/4803) and 27% (1080/3968) of patients in the MAC arm received human leukocyte antigen (HLA)-identical sibling (MRD) alloHSCT and matched unrelated donor (MUD) alloHSCT (p = 0.05 for both), respectively. In total, 72% (1103/1537) of patients in the RIC arm and 74% (3599/4837) of patients in the MAC arm received HLA-matched alloHSCT (p = 0.12). Peripheral blood stem cells (PBSC) were used as the stem cell source in 63% (1134/1814) of patients in the RIC arm and in 49% (2387/4847) of patients in the MAC arm (p = 0.06). In the remaining patients, BM was used as the stem cell source. T cell depletion (TCD) including ex vivo TCD and in vivo TCD with anti-thymocyte globulin or alemtuzumab, were performed in 44% (653/1470) of patients in the RIC arm and in 19% (896/4814) of patients in the MAC arm (p = 0.001).
Comparison of OS and EFS between RIC and MAC alloHSCT
Eight [12,14-20] and six trials [12,14,15,17-19] were available for OS and EFS analysis, respectively. Heterogeneity among the studies in terms of OS (I2 = 0%; p = 0.97) and EFS (I2 = 0%; p = 0.87) was not significant. The pooled effect showed no significant difference in OS (OR, 0.96; 95% CI, 0.84-1.08; p = 0.47) or EFS (OR, 0.88; 95% CI, 0.77-1.00; p = 0.05) between the RIC and MAC arms.
Comparison of RI and NRM between RIC and MAC alloHSCT
All studies were available for NRM and RI analysis. Heterogeneity among the studies in this regard was not significant (NRM: I2 = 0%, p = 0.59; RI: I2 = 0%, p = 0.91). RI was lower in the MAC arm (OR, 1.41; 95% CI, 1.24-1.59; p < 0.00001). NRM was not significantly different between the two arms (OR, 0.99; 95% CI, 0.87-1.13; p = 0.85).
Comparison of grade II-IV aGVHD and cGVHD between RIC and MAC alloHSCT
Seven [12,14,16-20] and six [12,15-19] studies were available for total (n = 6189) and extensive (n = 1501) cGVHD analysis, respectively. Heterogeneity among the studies was not significant for total (I2 = 31%; p = 0.19) or extensive (I2 = 8%; p = 0.36) cGVHD. Total cGVHD (OR, 1.10; 95% CI, 0.88-1.38; p = 0.38) and extensive cGVHD (OR, 1.01; 95% CI, 0.75-1.37; p = 0.95) were similar in the RIC and MAC arms. Seven [14-20] studies including 5563 AML/MDS patients were available for grade II-IV aGVHD analysis, and heterogeneity among the studies was significant (I2 = 77%; p = 0.0002). The pooled effect showed a significantly lower incidence of grade II-IV aGVHD in the RIC arm than in the MAC arm (OR, 0.59; 95% CI, 0.36-0.96; p = 0.03).
Publication bias
The results of the Begg’s and Egger’s tests showed no significant indication of publication bias (Figure 1). Therefore, it is unlikely that publication bias had a major influence on the pooled effects.
Figure 1.
Forest plots from a meta-analysis of transplantation outcomes for RIC compared to MAC arm.
Discussion
AlloHSCT represents a potentially curative therapeutic strategy for AML/MDS treatment [1,2,21]. For many years, MAC regimens were given at the maximum tolerable dose with the aim to eliminate tumor burden, clear host hematopoietic cells from the BM, and provide sufficient immunosuppression to allow successful donor cell engraftment before HSCT. However, these high-dose regimens result in considerable toxicity and GVHD, the two leading causes of death in recipients of alloHSCT. Given that GVHD contributes to the toxicity of preparative regimens [7,22], RIC regimens were proposed. The relatively low toxicity and lower incidence and severity of GVHD of RIC regimens allows their application to patients who are not suitable candidates for MAC alloHSCT because of advanced age or comorbidities [23].
The main finding of our study was that RIC and MAC yield similar outcomes (OS and EFS), even though patients in the RIC arm were elderly and thus, in worse general condition. In a retrospective study from the Gruppo Italiano Trapianto Di Midollo Osseo (GITMO), the conditioning regimen for alloHSCT (RIC vs. MAC) was found not to be significantly associated with 3-year OS in AML patients with active disease in both the univariate and multivariate analyses [24]. The EBMT reported that OS and leukemia-free survival (LFS) were not significantly different between RIC and MAC MRD alloHSCT in AML [25] and MDS [26] patients. Furthermore, updated data from this study are consistent with the original findings [12]. The EBMT reported that RIC and MAC MUD alloHSCT were associated with similar adjusted 2-year LFS rates in AML patients [27]. The CIBMTR suggested that MAC and RIC yield similar 5-year OS and disease-free survival (DFS) rates [14]. In the subgroup analysis, the adjusted 5-year DFS rate was 43% in the MAC arm, 37% in the RIC BM arm, and 33% in the RIC PBSC arm for AML patients in CR1 and MDS patients with < 5% BM blasts who were 40-60 years of age and had Karnofsky scores ≥ 90%. Although the adjusted 5-year DFS rate was higher in the MAC arm, this difference was not significant (vs. RIC BM, p = 0.46; vs. RIC PBSC, p = 0.06). Lioure [18] and Bornhäuser [15] conducted prospective randomized trials in 2012 to compare the outcomes between RIC and MAC alloHSCT in AML. In the Bornhäuser 2012 study, patients were well matched in terms of age, cytogenetic risk, induction therapy, and donor type, and the 3-year OS and DFS rates were similar in the RIC and MAC arms. In the Lioure 2012 study, patients were well matched in terms of baseline characteristics, complete remission rate, and donor type but not in terms of gender distribution (higher proportion of male patients in the MAC arm) and age (older age in the RIC arm). Nine-year OS and EFS rates were not significantly different between the MAC and RIC arms in this study (68% vs. 65.8% and 63.4% vs. 69.3%, respectively).
Disease relapse is the major cause of treatment failure after alloHSCT in patients with AML/MDS and is profoundly influenced by cytogenetics [28-30], disease status at HSCT [29,31], and treatment procedure [32,33]. RIC was associated with a worse RI than MAC, which was associated with the lower efficacy of RIC in eradicating malignant clonal cells [14,26]. Predictors of relapse risk after MAC alloHSCT in AML/MDS patients have been identified [34-40]. The association of these factors with relapse risk after RIC alloHSCT should be investigated as relapse risk factors may differ according to conditioning regimen. Manjappa et al. [40] recently reported that cytomegalovirus (CMV) reactivation after MRD alloHSCT with TCD was associated with a significantly lower risk of relapse for AML patients in the MAC, but not in the RIC, arm. This indicates that the risk profile might differ to some extent between these two arms.
Interestingly, the results of our analysis suggest that NRM was similar for RIC and MAC alloHSCT. The integrated score, which was developed by Versluis et al. [41], contains the most dominant parameters from the HCT-CI [42] and EBMT [43] scores and is useful in predicting NRM for AML patients in CR1 proceeding to RIC HSCT. In this new scoring system, the parameters associated with NRM include age at alloHSCT, patient and donor CMV status, unrelated donor, time interval to alloHSCT, and various comorbidities, whereas disease stage and donor-recipient sex combination, which are included in the EBMT score, are irrelevant. The CIBMTR reported that, although early NRM was less frequent for RIC than for MAC, the 3-year and 5-year NRM rates were similar for the two regimens [14]. The Bornhäuser 2012 study [15] reported that the 12-month cumulative incidence of NRM was 8% for RIC and 17% for MAC (p = 0.048). NRM at 3 years increased by 5% in the RIC arm and by 1% in the MAC arm; thus, similar rates of NRM in the two arms were reached at 3 years after transplantation (13% for RIC and 18% for MAC). The adjusted hazard ratio (HR) for the 3-year NRM rate was not significantly different between RIC and MAC in this study (HR, 0.62; 95% CI, 0.30-1.31; p = 0.22). It is possible that RIC is more advantageous than MAC in preventing early, but not late, NRM. Scoring systems such as the HCT-CI score [42], EBMT score [43], and integrated score [41] could be used to identify parameters predictive of early and late NRM in patients receiving RIC and MAC alloHSCT. The results of these studies and our analysis suggest that NRM is not favorable with RIC. However, RIC may still have a positive effect on NRM as most patients in these studies were not matched in terms of age or comorbidities. Thus, patients in the RIC arm may have been at a higher risk of NRM.
Various factors have been shown to increase the risk of aGVHD, including HLA mismatch, unrelated donor, older donor age, and sex mismatch [44-48]. Treatment-related procedures such as GVHD prophylaxis and TCD can also impact the incidence of aGHVD [49-51]. The CIBMTR reported that, for MRD alloHSCT, the incidence of grade II-IV aGVHD was significantly lower in the RIC PBSC arm than in the MAC PBSC with TBI arm (OR, 0.70; 95% CI, 0.56-0.88; p = 0.002), whereas the incidence was similar in the MAC PBSC with TBI and RIC BM arms (OR, 0.90; 95% CI, 0.54-1.49; p = 0.67) [52]. However, for MUD alloHSCT, both RIC PBSC (OR, 0.75; 95% CI, 0.57-1.00; p = 0.05) and RIC BM (OR, 0.47; 95% CI, 0.29-0.76; p = 0.002) were found to significantly lower the incidence of grade II-IV aGVHD compared with MAC PBSC with TBI. Risk profiles of cGVHD and aGHVD were similar; however, some notable differences were observed [13,47,53]. The EBMT reported that the stem cell source (PBSC vs. BM) does not influence cGVHD in AML patients in complete remission receiving MRD RIC alloHSCT (HR, 1.15; 95% CI, 0.78-1.69; p = 0.48) [13]. Arora et al., on behalf of the CIBMTR, developed a cGVHD risk score by analyzing the patient and transplantation characteristics of 5343 AML, acute lymphoblastic leukemia, chronic myeloid leukemia, and MDS patients receiving alloHSCT. Ten specific risk factors were validated; however, conditioning intensity before alloHSCT was found not to be a significant risk factor for cGVHD [53].
Our study has several limitations. First, the majority of eligible studies were retrospective in nature, which might have introduced some bias into our findings. Second, baseline patient characteristics (age, HCT-CI score, and disease status at HSCT) and treatment protocols (TCD) might have influenced survival outcomes, RI, and GVHD incidence in our analysis.
Conclusion
The results of our analysis suggest that RIC alloHSCT is an effective treatment strategy for AML/MDS patients who are not suitable candidates for MAC alloHSCT because of advanced age or comorbidities. However, heterogeneity in the baseline patient characteristics and treatment protocols may influence the outcomes of RIC alloHSCT in our analysis. Future randomized clinical trials are needed to further evaluate the efficacy of RIC alloHSCT in AML/MDS.
Acknowledgements
This study was supported by the Hubei Natural Science Foundation (grant number 2013CFB098).
Disclosure of conflict of interest
None.
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