Clinical significance of high-dose cytarabine added to cyclophosphamide/total-body irradiation in bone marrow or peripheral blood stem cell transplantation for myeloid malignancy

Background Addition of high-dose cytarabine (HDCA) to the conventional cyclophosphamide/total-body irradiation (CY/TBI) regimen significantly improved prognosis after cord blood transplantation (CBT) for adult acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS). The efficacy of HDCA in bone marrow or peripheral blood stem cell transplantation (BMT/PBSCT), however, has not yet been elucidated. Findings We conducted a cohort study to compare the prognosis of HDCA/CY/TBI (N = 435) and CY/TBI (N = 1667) in BMT/PBSCT for AML/MDS using a Japanese transplant registry database. The median age was 38 years, and 86.0 % of the patients had AML. Unrelated donors comprised 54.6 %, and 63.9 % of donors were human leukocyte antigen (HLA)-matched. Overall survival (OS) was not improved in the HDCA/CY/TBI group (adjusted hazard ratio (HR), 1.14; p = 0.13). Neutrophil engraftment was inferior (HR, 0.80; p < 0.01), and the incidence of hemorrhagic cystitis and thrombotic microangiopathy increased in HDCA/CY/TBI (HR, 1.47 and 1.60; p = 0.06 and 0.04, respectively), leading to significantly higher non-relapse mortality (NRM; HR, 1.48; p < 0.01). Post-transplant relapse and tumor-related mortality were not suppressed by the addition of HDCA. Conclusions This study indicated the inefficacy of HDCA/CY/TBI in BMT/PBSCT for AML/MDS. Our results should be validated in large-scale prospective studies. Electronic supplementary material The online version of this article (doi:10.1186/s13045-015-0201-x) contains supplementary material, which is available to authorized users.


Introduction
Cyclophosphamide/total-body irradiation (CY/TBI) is a widely known conventional myeloablative regimen in allogeneic hematopoietic cell transplantation (HCT) for adult acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS) [1][2][3], while regimens with stronger anti-leukemic effects have been sought to reduce post-transplant relapse [4]. Among them, the addition of high-dose cytarabine (HDCA) to CY/TBI may be promising; in our recent large-scale study, HDCA/CY/TBI significantly improved overall survival (OS) compared to CY/TBI by suppressing relapse without increasing severe adverse events or non-relapse mortality (NRM) in cord blood transplantation (CBT) for AML/MDS [5]. However, previous studies in a small cohort with mixed hematopoietic malignancies showed that HDCA/CY/TBI increased NRM after bone marrow transplantation (BMT) [6,7]. These results require validation using disease-specified and newer cohorts, in order to reflect the characteristics of each malignancy and the

Patients and methods
Data for adult patients (age ≥16 years) with AML and MDS who underwent allogeneic BMT or PBSCT from related (Rel) or unrelated (UR) donors as first HCT after CY/ TBI (CY, total 120 mg/kg; TBI, 10-12 Gy) or HDCA/CY/ TBI (CA, 2-3 g/m 2 twice a day for 2-3 days) [5] between January 1, 2000 and December 31, 2012, were obtained from the Japanese Transplant Registry Unified Management Program (TRUMP) [8]. UR-PBSCT and haploidentical HCT were not included because of the small number of patients. Donor-derived serum and/or erythrocytes were depleted from grafts in case of mismatched ABO blood type, and grafts were transplanted without T cell depletion. Our protocol complied with the Declaration of Helsinki, and it was approved by the TRUMP Data Management Committee and the Ethics Committee of Kyoto University. Each patient provided written informed consent. From the registry database, we extracted data on basic pre-transplant characteristics and post-transplant clinical courses. Disease risk was defined as previously reported [9]. Disparity in human leukocyte antigen (HLA)-A, B, and DR antigens was determined at the serologic level in Rel-BMT and Rel-PBSCT. In UR-BMT, 8 antigens including HLA-C were determined at the allele level; a 6/6 (Rel) or 8/8 (UR) match was considered HLA-matched [10]. Statistical analyses were performed as described previously [5].
OS of the HDCA/CY/TBI group was inferior to that of the CY/TBI group ( Fig. 1a; 59.3 vs 72.0 % at 1 year; 45.3 vs 58.8 % at 3 years after HCT). This difference was significant on univariate analysis ( Table 2), but not on multivariate analysis after adjustment for confounding factors (hazard ratio (HR), 1.14; p = 0.13; Table 3). In subgroup analyses according to pre-transplant characteristics, OS in the HDCA/ CY/TBI group was significantly inferior in standard-risk disease (HR, 1.52; p < 0.01). No significant differences were found in other subgroups (Additional file 1: Figure S1).
We compared the clinical courses that led to higher NRM in HDCA/CY/TBI, with a focus of engraftment, GVHD, infection, and other acute phase complications (Fig. 2). The HDCA/CY/TBI group showed significantly lower proportions of neutrophil and platelet engraftment following HCT (HR, 0.80; p < 0.01, and HR, 0.83; p < 0.01, respectively). Complete chimerism was achieved in 78.2 % of the CY/TBI group vs 72.6 % of the HDCA/ CY/TBI group (p = 0.04). We observed no significant differences in the incidence of acute or chronic GVHD (grades II-IV acute GVHD, 39.3 vs 38.2 %; chronic GVHD  (Fig. 2). Hemorrhagic cystitis, mostly due to viral reactivation or infection [11], and thrombotic microangiopathy (TMA) were more frequently observed in the HDCA/CY/TBI group (HR, 1.47; p = 0.06, and HR, 1.60; p = 0.04, respectively). These two   complications were related to a significantly higher proportion of NRM (data not shown). Other potential complications of HDCA, such as central nervous system (CNS) dysfunction and acute respiratory dysfunction syndrome (ARDS) [12], were not increased in the HDCA/ CY/TBI group.

Discussion
In this study on myeloablative BMT/PBSCT for AML/ MDS, we did not observe the improvement of OS in the HDCA/CY/TBI group due to (1) a higher proportion of NRM and (2) the lack of apparent additional anti-leukemic effect of HDCA. These results differ from those of CBT, in which a stronger anti-leukemic effect without increased NRM led to superior OS in HDCA/CY/TBI [5].
Among acute phase complications that can lead to NRM, hemorrhagic cystitis and TMA were increased after HDCA/CY/TBI. These complications, if not resolved early, can induce renal failure, prohibit immune reconstitution, and deteriorate patient's nutrition and performance status, which may ultimately lead to significantly higher NRM [11,13]. The strong cytotoxicity of HDCA combined with significantly poorer neutrophil engraftment might cause cystitis-related virus reactivation or vascular endothelial cell injury which can induce hemorrhagic cystitis or TMA. These features were not observed in CBT [5]; the relatively higher incidence of acute GVHD in BMT/PBSCT can explain this difference because both hemorrhagic cystitis and TMA are closely related to preceding acute GVHD [11,13].
On the other hand, no additional anti-leukemic effect of HDCA was apparent in this study. HDCA can reduce the remaining leukemia cells that may cause relapse after HCT [12]. This anti-leukemic effect of HDCA directly reduced the incidence of relapse in CBT [5] because graft-versus-leukemia (GVL) effects after CBT was relatively weak [14]; relapse after CBT mainly depends on the efficacy of conditioning regimens [5]. In BMT/ PBSCT, however, GVL effects are much stronger than CBT especially in the case of HLA-mismatched transplantation [14]. Suppression of total relapse after HCT is mainly attributed to continuous GVL effects [14] Tables 1 and 2 NRM non-relapse mortality * Indicates statistically significant compared to the conditioning regimens which will be inactivated rapidly after HCT [12]; strength of conditioning regimens (for example, HDCA addition in this study) may not directly influence on relapse reduction. These differences in GVL effects can partly explain the discrepancy in the efficacy of HDCA on post-transplant relapse or disease-related death. A larger proportion of patients with high-risk disease and worse performance status in the HDCA/CY/TBI group may confound the outcomes, but multivariate and subgroup analyses indicated unimproved prognosis in HDCA/CY/TBI even after eliminating those confounding factors. Moreover, subgroup analyses regarding the percentage of myeloblast just before conditioning regimens were carried out; no significant differences of OS between CY/TBI and HDCA/CY/TBI were found in any subgroups (data not shown). The bias in regard to the HCT centers, however, still remains to be overcome in this study. The choice of conditioning regimen depends on the attending physicians in each institution, indicating that the clinical experiences of each transplant center can be a confounding factor. Unfortunately, we were not able to adjust this factor because the database did not contain such information.
In summary, this study showed the inefficacy of adding HDCA to CY/TBI in BMT/PBSCT for AML/MDS, suggesting that the merits of HDCA in CBT cannot be extrapolated to BMT/PBSCT. Incidence of GVHD or strength of GVL effects may be related to these differences between donor sources. This single-country retrospective analysis should be validated in future prospective studies in order to determine proper conditioning regimens in BMT/PBSCT for AML/MDS.

Additional file
Additional file 1: Figure S1. Subgroup analyses of OS with respect to patient characteristics. OS was compared in each subgroup with respect to patient characteristics. The adjusted HRs of overall mortality in the HDCA/CY/TBI group were shown compared to the CY/TBI group. Black dots indicate HRs, and 95 %CI ranges are shown by black bars. Other abbreviations are explained in Tables 1-3 TMA thrombotic microangiopathy, VOD veno-occlusive disease, CNS central nervous system, ARDS acute respiratory distress syndrome Submit your manuscript at www.biomedcentral.com/submit