Reduced Intensity Conditioning Followed by Allogeneic Hematopoietic Stem Cell Transplantation Is a Good Choice for Acute Myeloid Leukemia and Myelodysplastic Syndrome: A Meta-Analysis of Randomized Controlled Trials

Background Reduced intensity conditioning (RIC) before allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been reported to have the same overall survival (OS) as myeloablative conditioning (MAC) for patients with acute myeloid leukemia (AML) in complete remission (CR) and myelodysplastic syndrome (MDS). However, results from different studies are conflicting. Therefore, we conducted a systematic review and meta-analysis guided by PRISMA 2009 to confirm the efficacy and safety of RIC vs. MAC for AML in CR and MDS. Methods We search PubMed, Web of Science, Embase, Cochrane central, clinical trial registries and related websites, major conference proceedings, and field-related journals from January 1, 1980, to July 1, 2020, for studies comparing RIC with MAC before the first allo-HSCT in patients with AML in CR or MDS. Only randomized controlled trials (RCTs) were included. OS was the primary endpoint and generic inverse variance method was used to combine hazard ratio (HR) and 95% CI. Results We retrieved 7,770 records. Six RCTs with 1,413 participants (711 in RIC, 702 in MAC) were included. RIC had the same OS (HR = 0.95, 95% CI 0.64–1.4, p = 0.80) and cumulative incidence of relapse as MAC (HR = 1.18, 95% CI 0.88–1.59, p = 0.28). Furthermore, RIC significantly reduced non-relapse mortality more than total body irradiation/busulfan-based MAC (HR = 0.53, 95% CI 0.36–0.80, p = 0.002) and had similar long-term OS and graft failure as MAC. Conclusion RIC conditioning regimens are recommended as an adequate option of preparative treatment before allo-HSCT for patients with AML in CR or MDS. Systematic Review Registration https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=185436.


Rationale
3 Describe the rationale for the review in the context of what is already known.

2-3
Objectives 4 Provide an explicit statement of questions being addressed with reference to participants, interventions, comparisons, outcomes, and study design (PICOS).

METHODS
Protocol and registration 5 Indicate if a review protocol exists, if and where it can be accessed (e.g., Web address), and, if available, provide 3 registration information including registration number.
Eligibility criteria 6 Specify study characteristics (e.g., PICOS, length of follow-up) and report characteristics (e.g., years considered, language, publication status) used as criteria for eligibility, giving rationale.

3-4
Information sources 7 Describe all information sources (e.g., databases with dates of coverage, contact with study authors to identify additional studies) in the search and date last searched.

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Search 8 Present full electronic search strategy for at least one database, including any limits used, such that it could be repeated.

Supplement 2
Study selection 9 State the process for selecting studies (i.e., screening, eligibility, included in systematic review, and, if applicable, included in the meta-analysis).

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Data collection process 10 Describe method of data extraction from reports (e.g., piloted forms, independently, in duplicate) and any processes for obtaining and confirming data from investigators. 4 Data items 11 List and define all variables for which data were sought (e.g., PICOS, funding sources) and any assumptions and simplifications made.

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Risk of bias in individual studies 12 Describe methods used for assessing risk of bias of individual studies (including specification of whether this was done at the study or outcome level), and how this information is to be used in any data synthesis.
Page 4, Table 2 and Supplement 3 Table 2 5 Additional analyses 16 Describe methods of additional analyses (e.g., sensitivity or subgroup analyses, meta-regression), if done, indicating which were pre-specified.

Study selection
17 Give numbers of studies screened, assessed for eligibility, and included in the review, with reasons for exclusions at each stage, ideally with a flow diagram.
Pages 5 and Figure 1 Study characteristics 18 For each study, present characteristics for which data were extracted (e.g., study size, PICOS, follow-up period) and provide the citations.  Our searching strategy was composed of the following three terms.
2. The "reduced intensity conditioning" terms: we used the following free words to comprehensively search the related words, "'reduc* or low or lower or less or lessen or lesser or decreas*' and 'condition* or prepar* or pretreat* or precondition*'" or "fludarabine or Flu or melphalan or Mel or RIC".
To identify RCT studies, we used the Cochrane highly sensitive search filters for identifying randomized trials in Medline and Embase.
We also searched conference proceedings from the European Hematology Association, Interventions RIC group: The reduced-intensity conditioning regimen was 0·8 mg/kg busulfan applied as 2-h infusion at 6-h intervals on days -4 and -3 with 30 mg/m² fl udarabine daily for 4 days (day −6 to −3). MAC group: Patients had treosulfan dose of 14 g/m² daily on days -6 to -4 of the 6-day regimen, was changed to 10 g/m² treosulfan daily applied as a 2-h infusion for 3 days (days -4 to -2) with 30 mg/m² fl udarabine daily for 4 days (day −6 to −3). GVHD prophylaxis: Prophylaxis for GvHD was standardised in both groups and based on ciclosporin from day -1 (5 mg/kg daily, concentration adapted) and short course methotrexate (15 mg/m² on day +1, and 10 mg/m² on days +3 and +6). All matched unrelated donors recipients received anti-T-lymphocyte immune globulin (either ATG Fresenius or Grafalon Neovii at a dose of 10 mg/kg on days -4, -3, and -2; or Thymoglobulin [Sanofi Genzyme] at a dose of 2·5 mg/kg on days -2 and -1).

Outcomes
The primary efficacy outcome: event-free survival 2 years after HSCT The secondary outcome: overall survival, cumulative incidence of relapse or progression, cumulative incidence of non-relapse mortality (probability of dying without relapse or progression), and cumulative incidence of acute and chronic GvHD within 2 years of transplantation; incidence of grade 3-4 mucositis and other grade 3-4 adverse events between day -6 and day +28 after transplantation; cumulative incidence of engraftment on day +28; and incidence of complete donor-type chimerism on days +28 and +100 after transplantation  Interventions RIC group: The reduced-intensity conditioning regimen was four 2 Gy doses of total-body irradiation (8 Gy) on days −3 and −2 with 30 mg/m² fl udarabine daily for 4 days (day −6 to −3). Total-body irradiation could also be done on days −6 and −5 if logistics prevented treatment on days −3 and −2. MAC group: Patients in the standard conditioning group had six 2 Gy doses of total-body irradiation (12 Gy) during 3 days (day −6 to −4; two doses per day) with lung shielding and 60 mg/kg cyclophosphamide per day for 2 days (days −3 and −2). A prophylactic infusion of mesna was given before and during cyclophosphamide treatment. GVHD prophylaxis: 20 mg/kg of ATG-Fresenius (Fresenius Biotech, Bad Homburg, Germany) was given on days −3 to −1 (cumulative dose 60 mg/kg). Ciclosporin from day -1, with target trough concentrations of 200 ng/mL or higher, and 15 mg/m² methotrexate on day 1 and 10 mg/m² on days 3, 6, and 11.

Outcomes
The primary efficacy outcome: the incidence of nonrelapse mortality The secondary outcome: overall survival, disease-free survival, relapse incidence, and incidence of acute and chronic graft-versus host disease.  RIC group: busulfan (8 mg/kg orally or 6.4 mg/kg intravenously) and fludarabine (150 mg/m2) MAC group: busulfan (16 mg/kg orally or 12.8 mg/kg intravenously) and cyclophosphamide (120 mg/kg) GVHD prophylaxis: cyclosporine and a short course of methotrexate (10 mg/m2 on days +1, +3, +6, and +11); In the case of unrelated donor antilymphocyte globulin (Fresenius, Graefelfing, Germany) at a cumulative does of 30 to 60 mg/kg or antithymocyte globulin (Thymoglobulin; Sanofi, Paris, France) at a cumulative dose of 6 to 10 mg/kg could be administered divided on days 23, 22, and 21 or alemtuzumab 100 mg divided on days 28 to 24 according to center policy; however, alemtuzumab was not used in a single patient. Outcomes The primary efficacy outcome: NRM after 1 year The secondary outcome: comparison of engraftment, toxicity, acute and chronic GVHD, infectious complications, and event-free survival and overall survival at 2 years.  Patients with cytogenetic favourable AML ("low risk") and in CR1, who did not present unfavourable features like secondary or therapy-related AML or insufficient response to AML induction therapy. MDS patients with IPSS-R "very low risk" or "low risk" at trial entry, who did not present unfavourable clinical features during disease history like refractory severe thrombocytopaenia with severe bleeding complications, life-threatening infectious complications due to severe neutropaenia and/or very high red blood cell transfusion requirement and related complications.

Outcomes
The primary efficacy outcome: Event-free survival (EFS) within 2 years after transplantation. Events were defined as relapse of disease, graft failure or death (whatever occurred first).
The secondary outcome: Relapse/progression incidence (RI) within 2 years of HSCT, Overall survival (OS), Non-relapse mortality (NRM), Transplantation-related mortality (TRM).  RIC group: fludarabine 30 mg m 2 day -1 for 6 days, combined with busulfan 4 mg kg -1 day -1 for 2 days in patients with AML and in two patients with CML. Further two patients with CML received fludarabine 30 mg m -2 day -1 for 3 days combined with 2 Gy total body irradiation (TBI) MAC group: busulfan 4 mg kg -1 day -1 administered in four doses for 4 days, combined with cyclophosphamide 120 mg kg -1 GVHD prophylaxis: Most patients received cyclosporine (CsA) combined with four doses of methotrexate. CsA was administered intravenously (i.v.) on day 1 and on day 0, followed by oral CsA at a dose ranging between 3 and 12 mg kg -1 . We aimed to achieve a trough level of 100 ng mL -1 in HLA-identical sibling transplantation for malignancies. CsA trough target levels were between 200 and 300 ng mL -1 in patients with a nonmalignant disorder and a sibling donor, and in all patients with MUDs. In two patients who were given fludarabine and 2 Gy TBI, CsA was combined with mycophenolate mofetil. Two patients in the RIC group were treated with tacrolimus (0.1 mg kg -1 day -1 orally), aiming at trough levels between 5 and 15 ng mL -1 , in combination with sirolimus (3-6 mg) to achieve a trough level of 5-10 ng mL -1 . Anti-thymocyte globulin (Thymoglobulin; Genzyme, Cambridge, MA, USA) at a dose of 6-8 mg kg -1 was given to all recipients of unrelated grafts and to four patients conditioned with RIC. Outcomes leukaemia-free survival, overall survival, TRM, GVHD and relapse rate  Interventions RIC group: fludarabine (120 to 180 mg/m 2 ) with busulfan (≤ 8 mg/kg orally or 6.4 mg/kg intravenously; Flu/Bu2) or melphalan (≤ 150 mg/m2; Flu/Mel) MAC group: busulfan (16 mg/kg orally or 12.8 mg/kg intravenously) with cyclophosphamide (120 mg/kg) or fludarabine (120 to 180 mg/m2; Flu/Bu4) or cyclophosphamide (120mg/kg) and total-body irradiation (12 to 14.2Gy) GVHD prophylaxis: included methotrexate 10 to 15 mg/m2 on day 1 and 5 to 10 mg/m 2 on days 3, 6, and 11 administered with cyclosporine or tacrolimus or tacrolimus with sirolimus or cyclosporine with mycophenolate mofetil. Experimental GVHD therapies were allowed provided they included a calcineurin inhibitor and no post-HCT cyclophosphamide or T-cell depletion. Antithymocyte globulin was allowed; however, its use was declared pre-random assignment, and it was administered regardless of conditioning intensity. Stem-cell sources were bone marrow or peripheralblood stem cells.

Outcomes
The primary efficacy outcome: OS at 18 months The secondary outcome: relapse-free survival (RFS), TRM, absolute neutrophil count (ANC) and platelet recovery, kinetics of donor cell engraftment, graft failure, GVHD, grade 3 to 4 toxicities, infections, and quality of life Quote: "Patients were randomly assigned at a one-to-one ratio to either MAC and RIC using permuted blocks of random sizes with stratification by center" Comment: Probably done.
Allocation concealment (selection bias) Low risk Quote: "Patients were randomly assigned at a one-to-one ratio to either MAC and RIC using permuted blocks of random sizes with stratification by center" Comment: Probably done.
Blinding of participants and personnel (performance bias) All outcomes Low risk Quote: "Patients and physicians were informed of the random assignment" Comment Probably not done.
Blinding of outcome assessment (detection bias) All outcomes Low risk Quote: "study investigators assigned to evaluate end points were blinded to each participant's random assignment.". Comment: Probably done.
Incomplete outcome data (attrition bias) All outcomes Low risk All randomized participants had the primary outcome data reported. Comment: Probably done.

Low risk
The primary and secondary outcomes were all reported. Comment: Probably done Other bias