Postremission Therapy for AML
A major challenge in the treatment of children with acute myeloid leukemia (AML) is to prolong the duration of the initial remission with additional chemotherapy or hematopoietic stem cell transplantation (HSCT). In practice, most patients are treated with intensive chemotherapy after remission is achieved, as only a small subset have a matched-family donor (MFD). Such therapy includes some of the drugs used in induction while also introducing non-cross–resistant drugs and commonly high-dose cytarabine. Studies in adults with AML have demonstrated that consolidation with a high-dose cytarabine regimen improves outcome compared with consolidation with a standard-dose cytarabine regimen, particularly in patients with inv(16) and t(8;21) AML subtypes.[1,2] Randomized studies evaluating the contribution of high-dose cytarabine to postremission therapy have not been conducted in children, but studies employing historical controls suggest that consolidation with a high-dose cytarabine regimen improves outcome compared with less intensive consolidation therapies.[3-5]
The optimal number of postremission courses of therapy remains unclear, but appears to require at least three courses of intensive therapy, including the induction course. A United Kingdom Medical Research Council (MRC) study randomly assigned adult and pediatric patients to four versus five courses of intensive therapy. Five courses did not show an advantage in relapse-free and overall survival (OS).[7,8][Level of evidence: 1iiA]
The use of HSCT in first remission has been under evaluation since the late 1970s, and evidence-based appraisals concerning indications for autologous and allogeneic HSCT have been published. Prospective trials of transplantation in children with AML suggest that overall 60% to 70% of children with HLA-matched donors available who undergo allogeneic HSCT during their first remission experience long-term remissions,[10,11] with the caveat that outcome following allogeneic HSCT is dependent upon risk-classification status. In prospective trials of allogeneic HSCT compared with chemotherapy and/or autologous HSCT, a superior disease-free survival (DFS) has been observed for patients who were assigned to allogeneic transplantation based on availability of a family 6/6 or 5/6 HLA-matched donor in adults and children.[10,11,13-17] However, the superiority of allogeneic HSCT over chemotherapy has not always been observed. Several large cooperative group clinical trials for children with AML have found no benefit for autologous HSCT over intensive chemotherapy.[10,11,13,15]
Current application of allogeneic HSCT involves incorporation of risk classification into the determination of whether transplantation should be pursued in first remission. Because of the improved outcome in patients with favorable prognostic features receiving contemporary chemotherapy regimens and the lack of demonstrable superiority for HSCT in this patient population, it is now recommended that this group of patients receive MFD HSCT only after first relapse and the achievement of a second complete remission (CR).[9,12,19,20]
There is conflicting evidence regarding the role of allogeneic HSCT in first remission for patients with intermediate-risk characteristics:
- A study combining the results of the POG-8821, CCG-2891, COG-2961, and MRC-Leuk-AML-10-Child studies identified a DFS and OS advantage for allogeneic HSCT in patients with intermediate-risk AML but not favorable-risk (inv(16) and t(8;21)) or poor-risk (del(5q), monosomy 5 or 7, or more than 15% blasts after first induction for POG/CCG studies), as well as including 3q abnormalities and complex cytogenetics in the MRC study. Weaknesses of this study include the large percentage of patients not assigned to a risk group and the relatively low EFS and OS rates for patients with intermediate risk assigned to chemotherapy compared with results observed in more recent clinical trials.[7,21]
- The AML99 clinical trial from the Japanese Childhood AML Cooperative Study Group observed a significant difference in DFS for intermediate risk patients assigned to MFD HSCT, but there was not a significant difference in OS.
- The AML-BFM 99 clinical trial demonstrated no significant difference for intermediate risk patients in either DFS or OS for patients assigned to MFD HSCT versus those assigned to chemotherapy.
Given the improved outcome for patients with intermediate-risk AML in recent clinical trials and the burden of acute and chronic toxicities associated with allogeneic transplantation, many childhood AML treatment groups (including the Children's Oncology Group [COG]) employ chemotherapy for intermediate-risk patients in first remission and reserve allogeneic HSCT for use following potential relapse.[7,22,23]
There are conflicting data regarding the role of allogeneic HSCT in first remission for patients with high-risk disease, complicated by the differing definitions of high risk used by different study groups.
- A retrospective analysis from COG and Center for International Blood and Marrow Transplant Research (CIBMTR) data on patients with AML and high-risk cytogenetics, defined as monosomy 7/del(7q), monosomy 5/del(5q), abnormalities of 3q, t(6;9), or complex karyotypes comparing chemotherapy only with minimal residual disease (MRD) donor and matched-unrelated donor (MUD) stem cell transplantation demonstrated no difference in the 5-year OS among the three treatment groups.
- A Nordic Society for Pediatric Hematology and Oncology study reported that time-intensive reinduction therapy followed by transplant with best available donor for patients whose AML did not respond to induction therapy resulted in 70% survival at a median follow-up of 2.6 years.[Level of evidence: 2A]
- A single-institution retrospective study of 50 consecutive patients (aged 0–30 years) with high-risk AML (FLT3-ITD, 11q23 MLL rearrangements, presence of chromosome 5 or 7 abnormalities, induction failure, persistent disease) reported a 5-year 72% OS and a 69% leukemia-free survival; they also reported a 17% treatment-related mortality.
- A subgroup analysis from the AML-BFM 98 clinical trial demonstrated improved survival rates for patients with 11q23 aberrations allocated to allogeneic HSCT, but not for patients without 11q23 aberrations.
- For children with FLT3-ITD (high allelic ratio), those who received MFD HSCT (n = 6) had higher OS than who received standard chemotherapy (n = 28); however the number of cases studied limited the ability to draw conclusions.
Many, but not all, pediatric clinical trial groups prescribe allogeneic HSCT for high-risk patients in first remission. For example, the COG frontline AML clinical trial (COG-AAML1031) prescribes allogeneic HSCT in first remission only for patients with predicted high risk of treatment failure based on unfavorable cytogenetic and molecular characteristics and elevated end-of-induction MRD levels. On the other hand, the AML-BFM 2004 clinical trial restricts allogeneic HSCT to patients in second CR and to refractory AML based on results from their AML-BFM 98 study showing no improvement in DFS or OS for high-risk patients receiving allogeneic HSCT in first CR and on the ability of HSCT in second CR to successfully treat a substantial proportion of patients.[18,28] Additionally, late sequelae (e.g., cardiomyopathy, skeletal anomalies, and liver dysfunction or cirrhosis) were increased for children undergoing allogeneic HSCT in first remission on the AML-BFM 98 study.
Because definitions of high-, intermediate-, and low-risk AML are evolving due to the ongoing association of molecular characteristics of the tumor with outcome (e.g., FLT-3 internal tandem duplications, WT1 mutations, and NPM1 mutations) as well as response to therapy (e.g., MRD assessments postinduction therapy), further analysis of subpopulations of patients treated with allogeneic HSCT will be an ongoing need in current and future clinical trials.
If transplant is chosen in first CR, the optimal preparative regimen and source of donor cells has not been determined, although alternative donor sources, including haploidentical donors, are being studied. Of note, there are no data that suggest total-body irradiation (TBI) is superior to busulfan-based myeloablative regimens.[18,19] A randomized trial comparing busulfan plus fludarabine versus busulfan plus cyclophosphamide as a preparative regimen for AML in first CR demonstrated that the former regimen was associated with less toxicity and comparable DFS and OS. In addition, a large prospective CIBMTR cohort study of children and adults with AML, myelodysplastic syndromes (MDS), and chronic myelogenous leukemia (CML) showed superior survival of patients with “early-stage” disease (chronic-phase CML, first CR AML, and MDS-refractory anemia) with busulfan-based regimens compared with TBI.
Maintenance chemotherapy has been shown to be effective in the treatment of acute promyelocytic leukemia. In other subtypes, there are no data that demonstrate that maintenance therapy given after intensive postremission therapy significantly prolongs remission duration. Maintenance chemotherapy failed to show benefit in two randomized studies,[3,32] and maintenance therapy with interleukin-2 also proved ineffective.Treatment Options Under Clinical Evaluation
The following are examples of national and/or institutional clinical trials that are currently being conducted. Information about ongoing clinical trials is available from the NCI Web site.
- AML08 (Clofarabine Plus Cytarabine Versus Conventional Induction Therapy and a Study of Natural Killer Cell Transplantation in Newly Diagnosed AML): St. Jude Children’s Research Hospital is conducting a randomized trial for children with newly diagnosed AML in which the efficacy of postchemotherapy NK cell transplantation is being assessed after five cycles of chemotherapy.
- COG-AAML1031 (Bortezomib and Sorafenib Tosylate in Patients With Newly Diagnosed AML With or Without Mutations): This is a phase III COG study designed to answer the question of whether the addition of the proteasome inhibitor bortezomib to chemotherapy during induction and postremission therapy improves outcome; in addition, this study will test whether the addition of sorafenib to chemotherapy along with HSCT for patients with high-allelic ratio FLT3-ITD–positive AML improves outcome compared with historical controls. This study will also utilize MRD determination at the end of induction, in addition to cytogenetics and molecular markers, to stratify postremission therapy.
Check for U.S. clinical trials from NCI's list of cancer clinical trials that are now accepting patients with childhood acute myeloid leukemia in remission. The list of clinical trials can be further narrowed by location, drug, intervention, and other criteria.
General information about clinical trials is also available from the NCI Web site.References
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