Impact of Conditioning Regimen on Outcomes for Children with Acute Myeloid Leukemia Undergoing Transplantation in First Complete Remission. An Analysis on Behalf of the Pediatric Disease Working Party of the European Group for Blood and Marrow Transplantation

Association between busulfan exposure and survival in patients undergoing a CD34+ selected stem cell transplantation

Busulfan is an alkylating drug routinely used in conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT). A myeloablative conditioning regimen, including busulfan, is commonly used in patients undergoing T-cell depletion (TCD) and allo-HCT, but data on optimal busulfan pharmacokinetic (PK) exposure in this setting are limited. Between 2012 and 2019, busulfan PK was performed to target an area under the curve exposure between 55 and 66 mg × h/L over 3 days using a noncompartmental analysis model. We retrospectively re-estimated busulfan exposure following the published population PK (popPK) model (2021) and correlated it with outcomes. To define optimal exposure, univariable models were performed with P splines, wherein hazard ratio (HR) plots were drawn, and thresholds were found graphically as the points at which the confidence interval crossed 1. Cox proportional hazard and competing risk models were used for analyses. 176 patients were included, with a median age of 59 years (range, 2-71). Using the popPK model, the median cumulative busulfan exposure was 63.4 mg × h/L (range, 46.3-90.7). The optimal threshold was at the upper limit of the lowest quartile (59.5 mg × h/L). 5-year overall survival (OS) with busulfan exposure ≥59.5 vs <59.5 mg × h/L was 67% (95% CI, 59-76) vs 40% (95% CI, 53-68), respectively (P = .02), and this association remained in a multivariate analyses (HR, 0.5; 95% CI, 0.29; 0.88; P = .02). In patients undergoing TCD allo-HCT, busulfan exposure is significantly associated with OS. The use of a published popPK model to optimize exposure may significantly improve the OS.

Impact of percutaneous endoscopic gastrostomy on pediatric bone marrow transplantation outcomes: Retrospectice single-center cohort study

BACKGROUND

Parenteral nutrition is commonly used to ensure nutrition support and prevent the harmful effects of malnutrition, which frequently occurs after allogeneic hematopoietic stem cell transplantation (aHSCT). Nevertheless, enteral nutrition supports the restoration of the gut barrier and microbiome as well as protects against infectious complications and acute graft-vs-host disease. Percutaneous endoscopic gastrostomy (PEG) may also be beneficial for gastric decompression and drug administration.

METHODS

We performed a retrospective cohort study to evaluate the impact of PEG on treatment outcomes in 75 children who underwent aHSCT with (n = 34) or without (n = 41) PEG from 2005 to 2016.

RESULTS

In 34 patients, PEG was used to ensure enteral nutrition support (n = 30), oral drug intake (n = 28), and abdominal decompression (n = 2). During the study period, we observed a beneficial association between PEG placement and transplant-related mortality as well as 5-year overall survival compared with the non-PEG group (12.9% vs 59.0%, P = 0.000; 85.3% vs 35.1%, P = 0.000, respectively). The beneficial impact of PEG was most prominent on 5-year overall survival in older children (12-17 years) with grafts from matched unrelated donors.

CONCLUSIONS

PEG placement had a positive association with transplant outcomes in pediatric patients undergoing aHSCT. To confirm these results, larger prospective studies are needed.

Efficacy of Azacitidine and Prophylactic Donor Lymphocyte Infusion after HSCT in Pediatric Patients with Acute Myelogenous Leukemia: A Retrospective Pre-Post Study

Pediatric patients with acute myeloid leukemia (AML) who undergo allogeneic hematopoietic stem cell transplantation (HSCT) continue to have high rates of relapse. In 2018, Phoenix Children's Hospital started using post-HSCT maintenance therapy in patients with AML in attempt to decrease the number of relapses after HSCT. This therapy consisted of the hypomethylating agent azacitidine (AZA; 6 cycles starting on day +60) and prophylactic donor lymphocyte infusion (DLI; 3 escalating doses beginning after day +120). We aimed to compare 2-year leukemia-free survival (LFS) post-HSCT between patients with AML who received post-HSCT maintenance therapy with AZA and prophylactic DLI and historical control patients who did not receive post-HSCT therapy. This retrospective pre-post study was conducted at Phoenix Children's Hospital and included patients with AML who underwent HSCT between January 1, 2008, and May 31, 2022. We compared LFS, overall survival (OS), and immune reconstitution patterns post-HSCT between patients with AML who received post-HSCT maintenance therapy with AZA and prophylactic DLI (postintervention group) and historical control patients who did not receive this post-HSCT maintenance therapy (preintervention group). Sixty-three patients were evaluable. After excluding 7 patients who died or relapsed prior to day +60, 56 patients remained, including 39 in the preintervention group and 17 in the postintervention group. The median age at transplantation was 9.1 years in the preintervention group and 11 years in the postintervention group (P = .33). The 2-year LFS was 61.5% in the preintervention group, compared to 88.2% in the postintervention group (P = .06). The 2-year OS was 69.2% in the preintervention group and 88.2% in the postintervention group (P = .15). The rates of CD3⁺CD4⁺ T cell and CD19⁺ B cell recovery were faster in the preintervention group compared to the postintervention group (P = .004 and .0006, respectively). In this limited retrospective study, post-HSCT maintenance therapy using AZA and prophylactic DLI was well tolerated; however, its efficacy is yet to be fully determined.

Busulfan, fludarabine, and melphalan are effective conditioning for pediatric and young adult patients with myeloid malignancies underdoing matched sibling or alternative donor transplantation

BACKGROUND

Allogeneic hematopoietic cell transplantation (allo-HCT) remains a curative option for patients with high-risk myeloid malignancies.

PROCEDURE

We present our 10-year experience (October 2012 to October 2021) of consecutive allo-HCT in patients with myeloid malignancies treated on the pediatric HCT service and conditioned with myeloablative targeted dose-busulfan (BU), fludarabine (FLU), and melphalan (MEL). Twenty-three children, adolescents, and young adult patients (CAYA) (median age 15.4 years) with acute myeloid leukemia (AML, n = 17), myelodysplastic syndrome (MDS, n = 4), or chronic myeloid leukemia (CML, n = 2) underwent allo-HCT post-BU-FLU-MEL. Four patients had treatment-related AML/MDS. Donor/stem cell source was matched sibling donor (MSD) PBSC (n = 7), matched unrelated donor (MUD) PBSC (n = 2), umbilical cord blood (UCB) (n = 3), or haploidentical-BMT (n = 11). Risk stratification was low (n = 2), intermediate (n = 15), high (n = 3), and very high risk (n = 1). The two patients with CML had failed tyrosine kinase inhibitor therapies.

RESULTS

With a median follow-up of 41.6 months, the relapse rate is only 4.5% with an overall survival (OS) 100%, progression-free survival (PFS) 95.5%, and graft-versus-host-free-relapse-free survival (GRFS) 67.8%. The donor source and the acute graft-versus-host disease (GvHD) prophylaxis regimen significantly impacted grade II-IV aGvHD 66.7% versus 19.2% (p = .039) and chronic graft-versus-host-disease (cGvHD) 66.7% versus 0% (p = .002) in the patients receiving MSD or MUD PBSC compared to haplo-BMT, respectively, resulting in improved GRFS in haplo-BMT, 83.3% compared to 40% matched donor peripheral blood stem cell transplant (PBSCT) (p = .025).

CONCLUSIONS

Our results demonstrate that BU-FLU-MEL is efficacious conditioning for disease control in young patients with myeloid malignancies undergoing MSD or alternative donor allo-HCT, but in the setting of PBSC grafts with cyclosporine A-methotrexate (CSA-MTX) GvHD prophylaxis, it results in an unacceptably high incidence of GvHD.

Rapid and accurate method for quantifying busulfan in plasma samples by isocratic liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Objectives

Administration of busulfan is extending rapidly as a part of a conditioning regimen in patients undergoing hematopoietic stem cell transplantation (HSCT). Monitoring blood plasma levels of busulfan is recommended for identifying the optimal dose in patients and for minimizing toxicity. The aim of this research was to validate a simple, rapid, and cost-effective analytical tool for measuring busulfan in human plasma that would be suitable for routine clinical use. This novel tool was based on liquid chromatography coupled to mass spectrometry.

Methods

Human plasma samples were prepared using a one-step protein precipitation protocol. These samples were then resolved by isocratic elution in a C18 column. The mobile phase consisted 2 mM ammonium acetate and 0.1% formic acid dissolved in a 30:70 ratio of methanol/water. Busulfan-d₈ was used as the internal standard.

Results

The run time was optimized at 1.6 min. Standard curves were linear from 0.03 to 5 mg/L. The coefficient of variation (%CV) was less than 8%. The accuracy of this method had an acceptable bias that fell within 85-115% range. No interference between busulfan and the interfering compound hemoglobin, lipemia, or bilirubin not even at the highest concentrations of compound was tested. Neither carryover nor matrix effects were observed using this method. The area under the plasma drug concentration-time curves obtained for 15 pediatric patients who received busulfan therapy prior to HSCT were analyzed and correlated properly with the administered doses.

Conclusions

This method was successfully validated and was found to be robust enough for therapeutic drug monitoring in a clinical setting.

Reduced-toxicity myeloablative conditioning regimen using fludarabine and full doses of intravenous busulfan in pediatric patients not eligible for standard myeloablative conditioning regimens: Results of a multicenter prospective phase 2 trial

Data regarding the safety and efficacy of reduced-toxicity conditioning regimen (RTC) prior to allogeneic stem cell transplantation (allo-SCT) to treat hematological malignancies in pediatric patients are limited. This prospective multicenter, phase 2 trial investigated a RTC regimen based on the combination of intravenous busulfan (3.2 mg/kg/d x 4 days), fludarabine (30 mg/m²/d x 5 days) and antithymocyte globulin (Thymoglobulin®, Genzyme; 5 mg/kg total dose) with the aim of delivering high dose myeloablation that would allow optimal disease control while minimizing toxicity, in a subgroup of children at very high risk of non-relapse mortality (NRM). The primary endpoint was NRM at 1 year after allo-SCT. A total of 48 high risk patients were included (median age, 13 years; range, 3-24). At 1 year, the cumulative incidence of recurrence/disease progression and NRM were 33% and 8%, respectively. With a median follow-up of 23 months, the Kaplan-Meier estimates of overall survival (OS) and disease-free survival (DFS) at 1 year were 69% and 58%, respectively. We conclude that the RTC regimen used in this prospective trial is safe, with a < 10% NRM rate noted among high-risk children and adolescents, paving the way for larger phase 3 trials incorporating novel agents pre- and post-allo-SCT.(ClinicalTrials.gov Identifier: NCT01572181).

Comparison of Pulmonary Toxicity after Total Body Irradiation- and Busulfan-Based Myeloablative Conditioning for Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Patients

Pulmonary toxicity after allogeneic hematopoietic stem cell transplantation (allo-HSCT) for childhood leukemia and myelodysplastic syndrome (MDS), along with the impact of different myeloablative conditioning regimens, remain incompletely described. Here we compared the acute and long-term incidence of pulmonary toxicity (PT) after total body irradiation (TBI)- and busulfan-based myeloablative conditioning. We conducted this retrospective cohort study of 311 consecutive pediatric patients with leukemia or MDS who underwent allo-HSCT at Dana-Farber Cancer Institute/Boston Children's Hospital between 2008 and 2018. PT was graded using Common Terminology Criteria for Adverse Events version 5.0. The primary objective was to compare the cumulative incidence of grade ≥3 and grade 5 PT after TBI-based and busulfan-based myeloablative conditioning using Gray's test. Secondary objectives were to determine factors associated with PT and overall survival (OS) using competing risk analysis and Cox regression analyses, respectively. There was no significant difference between the TBI-conditioned group (n = 227) and the busulfan-conditioned group (n = 84) in the incidence of grade ≥3 PT (29.2% versus 34.7% at 2 years; P = .26) or grade 5 pulmonary toxicity (6.2% versus 6.1% at 2 years; P = .47). Age (hazard ratio [HR], 1.70, 95% confidence interval [CI], 1.11 to 2.59; P = .01), grade ≥2 PT prior to allo-HSCT or preexisting pulmonary conditions (HR, 1.84, 95% CI, 1.24 to 2.72; P < .01), acute graft-versus-host disease (GVHD) (HR, 2.50; 95% CI, 1.51 to 4.14; P < .01), and chronic GVHD (HR, 2.61; 95% CI, 1.26 to 5.42; P = .01) were associated with grade ≥3 PT on multivariable analysis. Grade ≥3 PT was associated with worse OS (81.1% versus 61.5% at 2 years; P < .01). In pediatric allo-HSCT recipients, rates of PT were similar in recipients of TBI-based and recipients of busulfan-based myeloablative conditioning regimens. Age, the presence of PT or preexisting pulmonary conditions prior to transplantation, and the development of either acute or chronic GVHD were associated with grade ≥3 PT post-transplantation. Furthermore, the occurrence of grade 3-4 PT post-transplantation was associated with inferior OS.

Molecular Measurable Residual Disease Assessment before Hematopoietic Stem Cell Transplantation in Pediatric Acute Myeloid Leukemia Patients: A Retrospective Study by the I-BFM Study Group

Hematopoietic stem cell transplantation (HSCT) is a curative post-remission treatment in patients with acute myeloid leukemia (AML), but relapse after transplant is still a challenging event. In recent year, several studies have investigated the molecular minimal residual disease (qPCR-MRD) as a predictor of relapse, but the lack of standardized protocols, cut-offs, and timepoints, especially in the pediatric setting, has prevented its use in several settings, including before HSCT. Here, we propose the first collaborative retrospective I-BFM-AML study assessing qPCR-MRD values in pretransplant bone marrow samples of 112 patients with a diagnosis of AML harboring t(8;21)(q22; q22)RUNX1::RUNX1T1, or inv(16)(p13q22)CBFB::MYH11, or t(9;11)(p21;q23)KMT2A::MLLT3, or FLT3-ITD genetic markers. We calculated an ROC cut-off of 2.1 × 10⁻⁴ that revealed significantly increased OS (83.7% versus 57.1%) and EFS (80.2% versus 52.9%) for those patients with lower qPCR-MRD values. Then, we partitioned patients into three qPCR-MRD groups by combining two different thresholds, 2.1 × 10⁻⁴ and one lower cut-off of 1 × 10⁻², and stratified patients into low-, intermediate-, and high-risk groups. We found that the 5-year OS (83.7%, 68.6%, and 39.2%, respectively) and relapse-free survival (89.2%, 73.9%, and 67.9%, respectively) were significantly different independent of the genetic lesion, conditioning regimen, donor, and stem cell source. These data support the PCR-based approach playing a clinical relevance in AML transplant management.

ESTRO ACROP and SIOPE recommendations for myeloablative Total Body Irradiation in children

BACKGROUND AND PURPOSE

Myeloablative Total Body Irradiation (TBI) is an important modality in conditioning for allogeneic hematopoietic stem cell transplantation (HSCT), especially in children with high-risk acute lymphoblastic leukemia (ALL). TBI practices are heterogeneous and institution-specific. Since TBI is associated with multiple late adverse effects, recommendations may help to standardize practices and improve the outcome versus toxicity ratio for children.

MATERIAL AND METHODS

The European Society for Paediatric Oncology (SIOPE) Radiotherapy TBI Working Group together with ESTRO experts conducted a literature search and evaluation regarding myeloablative TBI techniques and toxicities in children. Findings were discussed in bimonthly virtual meetings and consensus recommendations were established.

RESULTS

Myeloablative TBI in HSCT conditioning is mostly performed for high-risk ALL patients or patients with recurring hematologic malignancies. TBI is discouraged in children <3-4 years old because of increased toxicity risk. Publications regarding TBI are mostly retrospective studies with level III-IV evidence. Preferential TBI dose in children is 12-14.4 Gy in 1.6-2 Gy fractions b.i.d. Dose reduction should be considered for the lungs to <8 Gy, for the kidneys to ≤10 Gy, and for the lenses to <12 Gy, for dose rates ≥6 cGy/min. Highly conformal techniques i.e. TomoTherapy and VMAT TBI or Total Marrow (and/or Lymphoid) Irradiation as implemented in several centers, improve dose homogeneity and organ sparing, and should be evaluated in studies.

CONCLUSIONS

These ESTRO ACROP SIOPE recommendations provide expert consensus for conventional and highly conformal myeloablative TBI in children, as well as a supporting literature overview of TBI techniques and toxicities.

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

Total body irradiation (TBI) has been a pivotal component of the conditioning regimen for allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) in very-high-risk acute lymphoblastic leukaemia (ALL) for decades, especially in children and young adults. The myeloablative conditioning regimen has two aims: (1) to eradicate leukaemic cells, and (2) to prevent rejection of the graft through suppression of the recipient's immune system. Radiotherapy has the advantage of achieving an adequate dose effect in sanctuary sites and in areas with poor blood supply. However, radiotherapy is subject to radiobiological trade-offs between ALL cell destruction, immune and haematopoietic stem cell survival, and various adverse effects in normal tissue. To diminish toxicity, a shift from single-fraction to fractionated TBI has taken place. However, HSCT and TBI are still associated with multiple late sequelae, leaving room for improvement. This review discusses the past developments of TBI and considerations for dose, fractionation and dose-rate, as well as issues regarding TBI setup performance, limitations and possibilities for improvement. TBI is typically delivered using conventional irradiation techniques and centres have locally developed heterogeneous treatment methods and ways to achieve reduced doses in several organs. There are, however, limitations in options to shield organs at risk without compromising the anti-leukaemic and immunosuppressive effects of conventional TBI. Technological improvements in radiotherapy planning and delivery with highly conformal TBI or total marrow irradiation (TMI), and total marrow and lymphoid irradiation (TMLI) have opened the way to investigate the potential reduction of radiotherapy-related toxicities without jeopardising efficacy. The demonstration of the superiority of TBI compared with chemotherapy-only conditioning regimens for event-free and overall survival in the randomised For Omitting Radiation Under Majority age (FORUM) trial in children with high-risk ALL makes exploration of the optimal use of TBI delivery mandatory. Standardisation and comprehensive reporting of conventional TBI techniques as well as cooperation between radiotherapy centres may help to increase the ratio between treatment outcomes and toxicity, and future studies must determine potential added benefit of innovative conformal techniques to ultimately improve quality of life for paediatric ALL patients receiving TBI-conditioned HSCT.

Pulmonary Toxicity After Total Body Irradiation - Critical Review of the Literature and Recommendations for Toxicity Reporting

INTRODUCTION

Total body irradiation is an effective conditioning regimen for allogeneic stem cell transplantation in pediatric and adult patients with high risk or relapsed/refractory leukemia. The most common adverse effect is pulmonary toxicity including idiopathic pneumonia syndrome (IPS). As centers adopt more advanced treatment planning techniques for TBI, total marrow irradiation (TMI), or total marrow and lymphoid irradiation (TMLI) there is a greater need to understand treatment-related risks for IPS for patients treated with conventional TBI. However, definitions of IPS as well as risk factors for IPS remain poorly characterized. In this study, we perform a critical review to further evaluate the literature describing pulmonary outcomes after TBI.

MATERIALS AND METHODS

A search of publications from 1960-2020 was undertaken in PubMed, Embase, and Cochrane Library. Search terms included "total body irradiation", "whole body radiation", "radiation pneumonias", "interstitial pneumonia", and "bone marrow transplantation". Demographic and treatment-related data was abstracted and evidence quality supporting risk factors for pulmonary toxicity was evaluated.

RESULTS

Of an initial 119,686 publications, 118 met inclusion criteria. Forty-six (39%) studies included a definition for pulmonary toxicity. A grading scale was provided in 20 studies (17%). In 42% of studies the lungs were shielded to a set mean dose of 800cGy. Fourteen (12%) reported toxicity outcomes by patient age. Reported pulmonary toxicity ranged from 0-71% of patients treated with TBI, and IPS ranged from 1-60%. The most common risk factors for IPS were receipt of a TBI containing regimen, increasing dose rate, and lack of pulmonary shielding. Four studies found an increasing risk of pulmonary toxicity with increasing age.

CONCLUSIONS

Definitions of IPS as well as demographic and treatment-related risk factors remain poorly characterized in the literature. We recommend routine adoption of the diagnostic workup and the definition of IPS proposed by the American Thoracic Society. Additional study is required to determine differences in clinical and treatment-related risk between pediatric and adult patients. Further study using 3D treatment planning is warranted to enhance dosimetric precision and correlation of dose volume histograms with toxicities.

The Role of Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) offers potentially curative treatment for many children with high-risk or relapsed acute leukemia (AL), thanks to the combination of intense preparative radio/chemotherapy and the graft-versus-leukemia (GvL) effect. Over the years, progress in high-resolution donor typing, choice of conditioning regimen, graft-versus-host disease (GvHD) prophylaxis and supportive care measures have continuously improved overall transplant outcome, and recent successes using alternative donors have extended the potential application of allotransplantation to most patients. In addition, the importance of minimal residual disease (MRD) before and after transplantation is being increasingly clarified and MRD-directed interventions may be employed to further ameliorate leukemia-free survival after allogeneic HSCT. These advances have occurred in parallel with continuous refinements in chemotherapy protocols and the development of targeted therapies, which may redefine the indications for HSCT in the coming years. This review discusses the role of HSCT in childhood AL by analysing transplant indications in both acute lymphoblastic and acute myeloid leukemia, together with current and most promising strategies to further improve transplant outcome, including optimization of conditioning regimen and MRD-directed interventions.

Extracorporeal Photopheresis in Children with Chronic Graft-Versus-Host Disease

Chronic graft versus host disease (cGVHD) remains a major complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). It significantly decreases survival and quality of life. The present study demonstrates retrospective data on extracorporeal photopheresis (ECP) in children with cGVHD. A total of 42 children with steroid-refractory cGVHD were enrolled in the study. The majority of patients had acute leukemia (n = 32, 76%). All patients received ECP as second (n = 18, 43%) or third (n = 24, 57%) line of therapy. Initial ECP schedule consisted of bimonthly regimen for two consecutive days with possibility of further tapering according to response. Any concurrent treatment administered before ECP could be continued if considered necessary. Complete response to ECP was registered in seven (17%) patients and partial response in 24 (57%). Overall response according to organ involvement was as follows: skin (n = 24, 75%), mucous membranes (n = 16, 73%), liver (n = 8, 80%), gut (n = 4, 80%), lungs (n = 2, 22%) and joints (n = 2, 67%). Five-year overall, progression-free and failure-free survival was 57%, 56% and 30%, respectively. Non-relapse mortality at 5 years was 14%. We didn't observe any clinically significant complications in children that could be attributed to the procedure. ECP remains important and safe treatment option in children with cGVHD.

Comparison of total body irradiation versus non-total body irradiation containing regimens for de novo acute myeloid leukemia in children

With limited data comparing hematopoietic cell transplant outcomes between myeloablative total body irradiation (TBI) containing and non-TBI regimens in children with de novo acute myeloid leukemia, the aim of this study was to compare transplant-outcomes between these regimens. Cox regression models were used to compare transplant-outcomes after TBI and non-TBI regimens in 624 children transplanted between 2008 and 2016. Thirty two percent (n=199) received TBI regimens whereas 68% (n=425) received non-TBI regimens. Five-year non-relapse mortality was higher with TBI regimens (22% vs. 11%, P<0.0001) but relapse was lower (23% vs. 37%, P<0.0001) compared to non-TBI regimens. Consequently, overall (62% vs. 60%, P=1.00) and leukemia-free survival (55% vs. 52%, P=0.42) did not differ between treatment groups. Grade 2-3 acute graft versus host disease was higher with TBI regimens (56% vs. 27%, P<0.0001) but not chronic graft versus host disease. The 3-year incidence of gonadal or growth hormone deficiency was higher with TBI regimens (24% vs. 8%, P<0.001) but there were no differences in late pulmonary, cardiac or renal impairment. In the absence of a survival advantage, the choice of TBI or non-TBI regimen merits careful consideration with the data favoring non-TBI regimens to limit the burden of morbidity associated with endocrine dysfunction.

Treatment of acute myeloid leukemia in children: A practical perspective

Pediatric acute myeloid leukemia (AML) is a heterogeneous disease that requires a multifaceted treatment approach. Although outcomes for low-risk AML have improved significantly over recent decades, high-risk AML continues to be associated with an adverse prognosis. Recent advances in molecular diagnostics, risk stratification, and supportive care have contributed to improvements in outcomes in pediatric AML. Targeted approaches, for example, the use of tyrosine kinase inhibitors to treat FLT3-ITD AML, offer promise and are currently undergoing clinical investigation in pediatric patients. New approaches to hematopoietic stem cell transplantation, including the use of haploidentical donors, are significantly expanding donor options for patients with high-risk AML. This review provides an overview of recent advances in the treatment of pediatric AML that are likely to have clinical impact and reshape the standard of care.

Late effects after ablative allogeneic stem cell transplantation for adolescent and young adult acute myeloid leukemia

There is marked paucity of data regarding late effects in adolescents and young adults (AYAs) who undergo myeloablative conditioning (MAC) allogeneic hematopoietic cell transplantation (HCT) for acute myeloid leukemia (AML). We evaluated late effects and survival in 826 1-year disease-free survivors of MAC HCT for AYA AML, with an additional focus on comparing late effects based upon MAC type (total body irradiation [TBI] vs high-dose chemotherapy only). The estimated 10-year cumulative incidence of subsequent neoplasms was 4% (95% confidence interval [CI], 2%-6%); 10-year cumulative incidence of nonmalignant late effects included gonadal dysfunction (10%; 95% CI, 8%-13%), cataracts (10%; 95% CI, 7%-13%), avascular necrosis (8%; 95% CI, 5%-10%), diabetes mellitus (5%; 95% CI, 3%-7%), and hypothyroidism (3%; 95% CI, 2%-5%). Receipt of TBI was independently associated with a higher risk of cataracts only (hazard ratio [HR], 4.98; P < .0001) whereas chronic graft-versus-host disease (cGVHD) was associated with an increased risk of cataracts (HR, 3.22; P = .0006), avascular necrosis (HR, 2.49; P = .006), and diabetes mellitus (HR, 3.36; P = .03). Estimated 10-year overall survival and leukemia-free survival were 73% and 70%, respectively, and did not differ on the basis of conditioning type. In conclusion, late effects among survivors of MAC HCT for AYA AML are frequent and are more closely linked to cGVHD than type of conditioning.

Aberrantly low STAT3 and STAT5 responses are associated with poor outcome and an inflammatory gene expression signature in pediatric acute myeloid leukemia

The relapse rate for children with acute myeloid leukemia is nearly 40% despite aggressive chemotherapy and often stem cell transplant. We sought to understand how environment-induced signaling responses are associated with clinical response to treatment. We previously reported that patients whose AML cells showed low G-CSF-induced STAT3 activation had inferior event-free survival compared to patients with stronger STAT3 responses. Here, we expanded the paradigm to evaluate multiple signaling parameters induced by a more physiological stimulus. We measured STAT3, STAT5 and ERK1/2 responses to G-CSF and to stromal cell-conditioned medium for 113 patients enrolled on COG trials AAML03P1 and AAML0531. Low inducible STAT3 activity was independently associated with inferior event-free survival in multivariate analyses. For inducible STAT5 activity, those with the lowest and highest responses had inferior event-free survival, compared to patients with intermediate STAT5 responses. Using existing RNA-sequencing data, we compared gene expression profiles for patients with low inducible STAT3/5 activation with those for patients with higher inducible STAT3/5 signaling. Genes encoding hematopoietic factors and mitochondrial respiratory chain subunits were overexpressed in the low STAT3/5 response groups, implicating inflammatory and metabolic pathways as potential mechanisms of chemotherapy resistance. We validated the prognostic relevance of individual genes from the low STAT3/5 response signature in a large independent cohort of pediatric AML patients. These findings provide novel insights into interactions between AML cells and the microenvironment that are associated with treatment failure and could be targeted for therapeutic interventions.

Azacitidine and prophylactic donor lymphocyte infusions after hematopoietic stem cell transplantation for pediatric high-risk acute myeloid leukemia

Post-hematopoietic stem cell transplantation (HSCT) maintenance therapy using azacitidine and prophylactic donor lymphocyte infusions (DLI) was implemented for high-risk acute myeloid leukemia. Azacitidine was started on day +60 as a 5 day course every 28 days for 6 cycles. DLI was given every 6 weeks for 3 doses starting after day +120. Ten patients were treated on this protocol. With a 90% one-year disease free survival, we report this post-HSCT maintenance therapy is feasible, safe, and well tolerated.

Hematopoietic cell transplant in pediatric acute myeloid leukemia after similar upfront therapy; a comparison of conditioning regimens

The impact of conditioning regimen prior to hematopoietic cell transplant (HCT) in pediatric AML-patients is not well studied. We retrospectively analyzed the impact of Busulfan-Cyclophosphamide (BuCy), Busulfan-Cyclophosphamide-Melphalan (BuCyMel) and Clofarabine-Fludarabine-Busulfan (CloFluBu) in pediatric AML-patients, with similar upfront leukemia treatment (NOPHO-DBHconsortium), receiving an HCT between 2010 and 2015. Outcomes of interest were LFS, relapse, TRM and GvHD. 103 patients were included; 30 received BuCy, 37 BuCyMel, and 36 CloFluBu. The 5-years LFS was 43.3% (SE ± 9.0) in the BuCy group, 59.2 % (SE ± 8.1) after BuCyMel, and 66.7 % (SE ± 7.9) after CloFluBu. Multivariable Cox regression analysis showed a trend to lower LFS after BuCy compared to CloFluBu (p = 0.07). BuCy was associated with a higher relapse incidence compared to the other regimens (p = 0.06). Younger age was a predictor for relapse (p = 0.02). A strong correlation between Busulfan Therapeutic Drug Monitoring (TDM) and lower incidence of aGvHD (p < 0.001) was found. In conclusion, LFS after BuCyMel and CloFluBu was comparable, lower LFS was found after BuCy, due to higher relapse incidence. CloFluBu was associated with lower incidence of aGvHD, suggesting lower toxicity with this type of conditioning. This finding is also explained by the impact of Busulfan monitoring.

Comparison of melphalan- And busulfan-based myeloablative conditioning in children undergoing allogeneic transplantation for acute myeloid leukemia or myelodysplasia

BACKGROUND

The optimal conditioning regimen for alloHCT in children with myeloid malignancies remains undefined.

PROCEDURE

We performed a retrospective review of children undergoing alloHCT for AML and MDS over a 10-year period (2008-2018) at our institution, comparing the outcomes of recipients of either a myeloablative busulfan- or reduced toxicity mel/thio-based conditioning regimen.

RESULTS

A total of 49 patients underwent alloHCT for AML/MDS (mel/thio, N = 21; busulfan, N = 28). Mel/thio recipients were selected due to pretransplant comorbidities. Recipients of mel/thio were more likely to have t-AML, and less likely to have MRD <0.1% at the time of alloHCT (57.1% vs 82.1%). Graft failure was more common in busulfan recipients; engraftment kinetics were similar between groups. Sinusoidal obstructive syndrome was diagnosed in 21% of busulfan and no mel/thio recipients (P = .03). One patient in each group died from TRM. Relapse incidence was comparable (mel/thio-29% vs busulfan-32%); however, relapse occurred significantly later in recipients of mel/thio conditioning (median d + 396 vs d + 137; P = .01). As a result, there was a trend toward improved OS at 1 and 3 years in mel/thio recipients (95% vs 74%, P = .06; and 75% vs 50%, P = .11; respectively).

CONCLUSION

In our single institution, when compared to myeloablative busulfan-based conditioning, use of a mel/thio-based reduced toxicity regimen resulted in comparable outcomes, despite higher risk patient and disease characteristics. Mel/thio recipients had both more comorbidities and higher risk disease profile, which did not translate into higher rates of either TRM or relapse.

The challenge of long-term follow-up of survivors of childhood acute leukemia after hematopoietic stem cell transplantation in resource-limited countries: A single-center report from Brazil

With the number of long-term HSCT survivors steadily increasing, attention needs to be focused on the late complications and quality of life. We therefore analyzed the outcome of 101 pediatric patients (<18 years old at the time of HSCT) transplanted for acute leukemia between 1981 and 2015 at Complexo Hospital de Clínicas, Federal University of Paraná, Brazil, and who survived at least two years after HSCT. The median follow-up was 5.9 years (2.0-29.0); median age at follow-up was 17.5 years (2.98-39.0). The 5-year cumulative incidence of relapse was 27.5% (95% CI 18.6%-36.4%). Two-year cumulative incidence of chronic GVHD was 21.8% (95% CI 13.7%-29.8%). Of the 101 patients, 72 patients (71.3%) presented with late effects. Those surviving longer after HSCT experienced more complications. Patients who received TBI-based regimen developed more late effects (P = .013) and more endocrinological complications (P = .024). Endocrinological complications were the most common late sequelae found in this study. For childhood survivors, quality of life was not influenced by age (at HSCT or at last visit), time from HSCT, gender, donor, or GVHD. For survivors that no longer were children, only age at last visit impacted financial domain measures, irrespective of gender, donor, or GVHD. The current study confirms the high burden late complications after pediatric HSCT have on the survivors and underlines the importance of extended follow-up.

Treosulfan-fludarabine-thiotepa-based conditioning treatment before allogeneic hematopoietic stem cell transplantation for pediatric patients with hematological malignancies

Treosulfan-based conditioning prior to allogeneic transplantation has been shown to have myeloablative, immunosuppressive, and antineoplastic effects associated with reduced non-relapse mortality (NRM) in adults. Therefore, we prospectively evaluated the safety and efficacy of treosulfan-based conditioning in children with hematological malignancies in this phase II trial. Overall, 65 children with acute lymphoblastic leukemia (35.4%), acute myeloid leukemia (44.6%), myelodysplastic syndrome (15.4%), or juvenile myelomonocytic leukemia (4.6%) received treosulfan intravenously at a dose of 10 mg/m²/day (7.7%), 12 g/m²/day (35.4%), or 14 g/m²/day (56.9%) according to their individual body surface area in combination with fludarabine and thiotepa. The incidence of complete donor chimerism at day +28 was 98.4% with no primary and only one secondary graft failure. At 36 months, NRM was only 3.1%, while relapse incidence was 21.7%, and overall survival was 83.0%. The cumulative incidence of acute graft-vs.-host disease was 45.3% for grades I–IV and 26.6% for grades II–IV. At 36 months, 25.8% overall and 19.4% moderate/severe chronic graft-vs.-host disease were reported. These data confirm the safe and effective use of treosulfan-based conditioning in pediatric patients with hematological malignancies. Therefore, treosulfan/fludarabine/thiotepa can be recommended for myeloablative conditioning in children with hematological malignancies.

Low-dose azacitidine for relapse prevention after allogeneic hematopoietic cell transplantation in children with myeloid malignancies

BACKGROUND

The prognosis of children who relapse after allogeneic hematopoietic cell transplant (alloHCT) for myeloid malignancies remains poor.

PROCEDURE

To describe the safety and feasibility of post-transplant azacitidine for relapse prevention, we retrospectively reviewed the charts of 18 children undergoing alloHCT for myeloid malignancies.

RESULTS

There were 15 evaluable patients since three patients did not receive planned azacitidine due to early relapse or TRM. Azacitidine (32 mg/m² /dose for 5 days, in 28-day cycles as tolerated up to 1 year post-transplant) was started at a median of 66 days post-transplant (range 42-118). Two-thirds (10/15) of patients received eight or more cycles. Five patients stopped therapy early, only one attributable to toxicity. Mild myelosuppression was the most common reason for cycle delays. Dose modifications were made in three patients. There were three relapses, two of which occurred in patients in CR2 and one in CR1, with a median follow-up of 20 months (range 12.5-28), and no TRM in patients who received azacitidine.

CONCLUSIONS

Post-transplant azacitidine in children is safe and feasible, with most patients successfully receiving all planned cycles. Despite the limitations of a small cohort, low relapse incidence suggests a potential benefit in disease control that warrants further investigation.

Comparison of conditioning regimens for autologous stem cell transplantation in children with acute myeloid leukemia: A nationwide retrospective study in Japan

BACKGROUND

Indications for hematopoietic stem cell transplantation (HSCT) have decreased with the improvement in chemotherapy for pediatric acute myeloid leukemia (AML) in the last decade. We conducted reevaluation of autologous HSCT (AHSCT) to compare myeloablative conditioning (MAC) regimens for pediatric AML without the need for consideration of toxicities caused by allogeneic immune reactions.

PROCEDURE

This retrospective study analyzed the clinical outcomes of 220 children with AML who underwent consecutive AHSCT between 1989 and 2002 in Japan by the national prospective registry. The transplantation outcomes of various conditioning regimens were compared.

RESULTS

The median follow-up period of the survivors was 160 months. The clinical outcomes of busulfan + cyclophosphamide ± etoposide or busulfan + melphalan regimens were significantly superior compared with other busulfan-based and total body irradiation-based regimens (leukemia-free survival [LFS]: 68% vs 42% and 55%, P = 0.001; overall survival [OS]: 74% vs 49% and 61%, P < 0.001). Multivariate analysis showed that busulfan + cyclophosphamide ± etoposide and busulfan + melphalan regimens were independent favorable factors for LFS (hazard ratio: 0.46; P < 0.001) and OS (hazard ratio: 0.40; P < 0.001) compared with the other busulfan-based regimen, and both age 2 years or older and advanced stage at AHSCT were independent poor predictors for LFS and OS, simultaneously.

CONCLUSION

Busulfan + cyclophosphamide ± etoposide and busulfan + melphalan regimens exhibited superior antileukemic effects compared with other BU-based myeloablative regimens.

The effect of N-acetyl-l-cysteine (NAC) on liver toxicity and clinical outcome after hematopoietic stem cell transplantation

Busulphan (Bu) is a myeloablative drug used for conditioning prior to hematopoietic stem cell transplantation. Bu is predominantly metabolized through glutathione conjugation, a reaction that consumes the hepatic glutathione. N-acetyl-l-cysteine (NAC) is a glutathione precursor used in the treatment of acetaminophen hepatotoxicity. NAC does not interfere with the busulphan myeloablative effect. We investigated the effect of NAC concomitant treatment during busulphan conditioning on the liver enzymes as well as the clinical outcome. Prophylactic NAC treatment was given to 54 patients upon the start of busulphan conditioning. These patients were compared with 54 historical matched controls who did not receive NAC treatment. In patients treated with NAC, aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) were significantly (P < 0.05) decreased after conditioning compared to their start values. Within the NAC-group, liver enzymes were normalized in those patients (30%) who had significantly high start values. No significant decrease in enzyme levels was observed in the control group. Furthermore, NAC affected neither Bu kinetics nor clinical outcome (sinusoidal obstruction syndrome incidence, graft-versus-host disease and/or graft failure). In conclusion: NAC is a potential prophylactic treatment for hepatotoxicity during busulphan conditioning. NAC therapy did not alter busulphan kinetics or affect clinical outcome.

Impact of graft-versus-host disease on relapse and survival after allogeneic stem cell transplantation for pediatric leukemia

Graft-versus-host disease (GVHD) occasionally leads to morbidity and mortality but is thought to reduce the risk of relapses in patients with a hematological malignancy. However, information on the effect of GVHD in pediatric leukemia is limited. Using a nationwide registry, we retrospectively analyzed 1526 children who underwent allogeneic stem cell transplantation for leukemia. Grades 0-I acute GVHD were associated with a higher relapse rate at three years after transplantation, at 25.4 and 24.3%, respectively, than grades II, III, or IV acute GVHD at 18.9%, 21.2%, and 2.6%, respectively. In contrast, the overall survival curve of the grades 0 and I GVHD groups (79.0% and 79.5%, respectively) approximated that of the grade II GVHD group (76.3%), and the probability of survival was worst in the severe GVHD groups (66.9% for grade III and 42.5% for grade IV). Chronic GVHD also reduced the relapse risk but conferred no survival advantage. Acute lymphoblastic leukemia was more sensitive to acute GVHD than acute myeloid leukemia (AML) while AML was more sensitive to chronic GVHD. Our study reproduced the preventive effects of GVHD against pediatric leukemia relapses but failed to demonstrate a significant survival advantage.

Treosulfan, Fludarabine, and Low-Dose Total Body Irradiation for Children and Young Adults with Acute Myeloid Leukemia or Myelodysplastic Syndrome Undergoing Allogeneic Hematopoietic Cell Transplantation: Prospective Phase II Trial of the Pediatric Blood and Marrow Transplant Consortium

This multicenter study evaluated a treosulfan-based regimen in children and young adults with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) undergoing allogeneic hematopoietic cell transplant (HCT). Forty patients with median age 11 years (range, 1 to 19) underwent allogeneic HCT for AML in first (n = 18), second (n = 11), and third or greater remission (n = 3) or MDS (n = 8) using bone marrow (n = 25), peripheral blood stem cells (n = 5), or cord blood (n = 9). The regimen consisted of body surface area (BSA)-based treosulfan 10 g/m²/day (BSA ≤ .5 m²), 12 g/m²/day (BSA > .5 to 1.0 m²), or 14 g/m²/day (BSA > 1.0 m²) on days -6 to -4; fludarabine 30 mg/m²/day on days -6 to -2; and a single fraction of 200 cGy total body irradiation on day -1. Graft-versus-host disease (GVHD) prophylaxis included tacrolimus and methotrexate for marrow and peripheral blood stem cell and cyclosporine/mycophenolate mofetil for cord blood. One-year overall survival, disease-free survival, and nonrelapse mortality were 80%, 73%, and 3%, respectively. One-year relapse was 38% for AML and 13% for MDS. No serious organ toxicities were observed. All 37 assessable patients engrafted. Cumulative incidences of grades II to IV acute GVHD and chronic GVHD were 22% and 40%, respectively. BSA-based treosulfan dosing resulted in predictable area under the curve and maximum concentration, which is required for dosing without measuring individual pharmacokinetic parameters. Observed differences in pharmacokinetics did not impact disease control or regimen toxicity. This BSA-based treosulfan regimen resulted in excellent engraftment and disease-free survival and minimal toxicity and transplant-related mortality (3%) in children and young adults with AML and MDS.

Umbilical Cord Blood Transplantation in Children with Acute Leukemia: Impact of Conditioning on Transplantation Outcomes

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN 0501) randomized children with hematologic malignancies to transplantation with 1 or 2 cord blood units (UCB) between 2006 and 2012. While the trial concluded that survival was similar regardless of number of units infused, survival was better than previously reported. This prompted a comparison of survival of trial versus nontrial patients to determine the generalizability of trial results and whether survival was better because of the trial treatment regimen. During the trial period, 396 recipients of a single UCB unit met trial eligibility but were not enrolled. Trial patients (n = 100) received total body irradiation (TBI) 1320 cGy, cyclophosphamide 120 mg/kg, and fludarabine 75 mg/m² (TCF). Nontrial patients either received the same regimen (n = 62; nontrial TCF) or alternative regimens (n = 334; nontrial regimens). Five-year survival between trial and nontrial patients conditioned with TCF was similar (70% versus 62%). However, 5-year survival was significantly lower with nontrial TBI-containing (47%; hazard ratio [HR], 1.97; P = .001) and chemotherapy-only regimens (49%; HR, 1.87; P = .007). The results of BMT CTN 0501 appear generalizable to the population of trial-eligible patients. The survival difference between the trial-specified regimen and other regimens indicate the importance of conditioning regimen for UCB transplantation.