Adult Acute Myeloid Leukemia in Remission
Although individual patients have been reported to have long disease-free survival (DFS) or cure with a single cycle of chemotherapy, postremission therapy is always indicated in therapy that is planned with curative intent. In a small randomized study conducted by the Eastern Cooperative Oncology Group (ECOG), all patients who did not receive postremission therapy experienced a relapse after a short median complete remission duration. Current approaches to postremission therapy include short-term, relatively intensive chemotherapy with cytarabine-based regimens similar to standard induction clinical trials (postremission chemotherapy), postremission chemotherapy with more dose-intensive cytarabine-based treatment, high-dose chemotherapy or chemoradiation therapy with autologous bone marrow rescue, and high-dose marrow-ablative therapy with allogeneic bone marrow rescue. While older studies have included longer-term therapy at lower doses (maintenance), no convincing evidence is available with acute myeloid leukemia (AML) that maintenance therapy provides prolonged disease-free survival (DFS) beyond shorter-term, more dose-intensive approaches, and few current treatment clinical trials include maintenance therapy.
Nontransplant postremission therapy using cytarabine-containing regimens has treatment-related death rates that are usually less than 10% to 20% and have yielded reported long-term DFS rates from 20% to 50%.[3-6] A large randomized trial that compared three different cytarabine-containing postremission therapy regimens showed a clear benefit in survival to patients younger than 60 years who received high-dose cytarabine. Intensification of cytarabine dose or duration of postremission chemotherapy with conventionally dosed cytarabine did not improve disease-free or OS in patients aged 60 years or older, as evidenced in the Medical Research Council (MRC-LEUK-AML11) trial.[7,8] The duration of postremission therapy has ranged from one cycle [4,6] to four or more cycles.[3,5] The optimal doses, schedules, and duration of postremission chemotherapy have not been determined. Therefore, to address these issues, patients with AML should be included in clinical trials at institutions that treat large numbers of such patients.
Dose-intensive cytarabine-based chemotherapy can be complicated by severe neurologic  and/or pulmonary toxic effects  and should be administered by physicians experienced in these regimens at centers that are equipped to deal with potential complications. In a retrospective analysis of 256 patients who received high-dose bolus cytarabine at a single institution, the most powerful predictor of cytarabine neurotoxicity was renal insufficiency. The incidence of neurotoxicity was significantly greater in patients treated with twice daily doses of 3 g/m2/dose when compared with 2 g/m2/dose.
Allogeneic bone marrow transplantation (BMT) results in the lowest incidence of leukemic relapse, even when compared with BMT from an identical twin (syngeneic BMT). This has led to the concept of an immunologic graft-versus-leukemia effect, similar to (and related to) graft-versus-host disease. The improvement in freedom from relapse using allogeneic BMT as the primary postremission therapy is offset, at least in part, by the increased morbidity and mortality caused by graft-versus-host disease, veno-occlusive disease of the liver, and interstitial pneumonitis. The DFS rates using allogeneic transplantation in first complete remission have ranged from 45% to 60%.[11-13] The use of allogeneic BMT as primary postremission therapy is limited by the need for a human leukocyte antigen (HLA)-matched sibling donor and the increased mortality from allogeneic BMT of patients who are older than 50 years. The mortality from allogeneic BMT that uses an HLA-matched sibling donor ranges from 20% to 40%, depending on the series. The use of matched, unrelated donors for allogeneic BMT is being evaluated at many centers but has a very substantial rate of treatment-related mortality, with DFS rates less than 35%. Retrospective analysis of data from the International Bone Marrow Transplant Registry suggests that postremission chemotherapy does not lead to an improvement in DFS or OS for patients in first remission undergoing allogeneic BMT from an HLA-identical sibling.[Level of evidence: 3iiiA]
A common clinical trial design used to evaluate the benefit of allogeneic transplant as consolidation therapy for AML in first remission is the so-called donor-no donor comparison. In this design, newly diagnosed AML patients who achieve a complete remission (CR1), have one or more siblings, and are deemed medically eligible for allogeneic transplant undergo HLA typing. If a sibling donor is identified, the patient is allocated to the transplantation arm. Analysis of outcome is by intention to treat; that is, patients assigned to the donor arm who do not receive a transplant are grouped in the analysis with the patients who did actually receive a transplant. Relapse-free survival (RFS) is the usual endpoint for this type of trial. Overall survival (OS) from the time of diagnosis is less frequently reported in these trials. Results of these trials have been mixed, with some trials showing a clear benefit across all cytogenetic subgroups, and others showing no benefit.
Investigators attempted to address this issue with a meta-analysis using data from 18 separate prospective trials of AML patients using the donor-no donor design, with data from an additional six trials included for sensitivity analysis. The trials included in this meta-analysis enrolled adult patients aged 60 and younger during the years 1982 to 2006. Median follow-up ranged from 42 months to 142 months. Preparative regimens were similar among the different trials. Allogeneic transplant was compared to autologous transplant (6 trials) or to a variety of consolidation chemotherapy regimens with high-dose cytarabine being the most common.
Treatment-related mortality ranged from 5% to 42% in the donor groups compared with 3% to 27% in the no-donor group. Of 18 trials reporting RFS across all cytogenetic risk groups, the combined hazard ratio (HR) for overall RFS benefit with allogeneic transplant was 0.80, indicating a statistically significant reduction in death or relapse in CR1. Of the 15 trials reporting OS across all cytogenetic risk groups, the combined HR for OS was 0.90, again indicating a statistically significant reduction in death or relapse in CR1.
In subgroup analysis according to cytogenetic risk category, there was no RFS or OS benefit of allogeneic transplant for patients with good-risk AML (RFS: HR, 1.07; 95% confidence interval [CI], 0.83–1.38; P = .59; OS: HR, 1.06; 95% CI, 0.64–1.76; P = .81). However, a transplant benefit was seen for patients with intermediate (RFS: HR, 0.83; 95% CI, 0.74–0.93; P < .01; OS: HR, 0.84; 95% CI, 0.71–0.99; P = .03) or poor-risk cytogenetics (RFS: HR, 0.73; 95% CI, 0.59–0.90; P < .01; OS: HR, 0.60; 95% CI, 0.40–0.90; P = .01). The conclusion from this meta-analysis was that allogeneic transplant from a sibling donor in CR1 is justified on the basis of improved RFS and OS for patients with intermediate- or poor-risk, but not good-risk, cytogenetics.[Level of evidence: 2A]
An important caveat to this analysis is that induction and postremission strategies for AML among studies included in the meta-analysis were not uniform; nor were definitions of cytogenetic risk groups uniform. This may have resulted in inferior survival rates among chemotherapy-only treated patients. Most U.S. leukemia physicians agree that transplantation should be offered to AML patients in CR1 in the setting of poor-risk cytogenetics and should not be offered to patients in CR1 with good-risk cytogenetics.
The use of matched, unrelated donors for allogeneic BMT is being evaluated at many centers but has a very substantial rate of treatment-related mortality, with DFS rates less than 35%. Retrospective analysis of data from the International Bone Marrow Transplant Registry suggests that postremission chemotherapy does not lead to an improvement in DFS or OS for patients in first remission undergoing allogeneic BMT from an HLA-identical sibling.[Level of evidence: 3iiiA]
Autologous BMT yielded DFS rates between 35% and 50% in patients with AML in first remission. Autologous BMT has also cured a smaller proportion of patients in second remission.[17-23] Treatment-related mortality rates of patients who have had autologous peripheral blood or marrow transplantation range from 10% to 20%. Ongoing controversies include the optimum timing of autologous stem cell transplantation, whether it should be preceded by postremission chemotherapy, and the role of ex vivo treatment of the graft with chemotherapy, such as 4-hydroperoxycyclophosphamide (4-HC)  or mafosphamide, or monoclonal antibodies, such as anti-CD33. Purged marrows have demonstrated delayed hematopoietic recovery; however, most studies that use unpurged marrow grafts have included several cycles of postremission chemotherapy and may have included patients who were already cured of their leukemia.
In a prospective trial of patients with AML in first remission, City of Hope investigators treated patients with one course of high-dose cytarabine postremission therapy, followed by unpurged autologous BMT following preparative therapy of total-body radiation therapy, etoposide, and cyclophosphamide. In an intent-to-treat analysis, actuarial DFS was approximately 50%, which is comparable to other reports of high-dose postremission therapy or purged autologous transplantation.[Level of evidence: 3iiDii]
A randomized trial by ECOG and the Southwest Oncology Group (SWOG) compared autologous BMT using 4-HC-purged bone marrow with high-dose cytarabine postremission therapy. No difference in DFS was found between patients treated with high-dose cytarabine, autologous BMT, or allogeneic BMT; however, OS was superior for patients treated with cytarabine compared with those who received BMT.[Level of evidence: 1iiA]
A randomized trial has compared the use of autologous BMT in first complete remission to postremission chemotherapy, with the latter group eligible for autologous BMT in second complete remission. The two arms of the study had equivalent survival. Two randomized trials in pediatric AML have shown no advantage of autologous transplantation following busulfan/cyclophosphamide preparative therapy and 4HC-purged graft when compared with postremission chemotherapy including high-dose cytarabine.[27,28] An additional randomized Groupe Ouest Est d'etude des Leucemies et Autres Maladies du Sang trial (NCT01074086) of autologous BMT versus intensive postremission chemotherapy in adult AML, using unpurged bone marrow, showed no advantage to receiving autologous BMT in first remission. Certain subsets of AML may specifically benefit from autologous BMT in first remission. In a retrospective analysis of 999 patients with de novo AML treated with allogeneic or autologous BMT in first remission in whom cytogenetic analysis at diagnosis was available, patients with poor-risk cytogenetics (abnormalities of chromosomes 5, 7, 11q, or hypodiploidy) had less favorable outcomes following allogeneic BMT than patients with normal karyotypes or other cytogenetic abnormalities. Leukemia-free survival for the patients in the poor-risk groups was approximately 20%.[Level of evidence: 3iiiDii]
An analysis of the SWOG/ECOG (E-3489) randomized trial of postremission therapy according to cytogenetic subgroups suggested that in patients with unfavorable cytogenetics, allogeneic BMT was associated with an improved relative risk of death, whereas in the favorable cytogenetics group, autologous transplantation was superior. These data were based on analysis of small subsets of patients and were not statistically significant. While secondary myelodysplastic syndromes have been reported following autologous BMT, the development of new clonal cytogenetic abnormalities following autologous BMT does not necessarily portend the development of secondary myelodysplastic syndromes or AML.[Level of evidence: 3iiiDiv] Whenever possible, patients should be entered on clinical trials of postremission management.
Because BMT can cure about 30% of patients who experience relapse following chemotherapy, some investigators suggested that allogeneic BMT can be reserved for early first relapse or second complete remission without compromising the number of patients who are ultimately cured; however, clinical and cytogenetic information can define certain subsets of patients with predictable better or worse prognoses using postremission chemotherapy. Good-risk factors include t(8; 21), inv(16) associated with M4 AML with eosinophilia, and t(15; 17) associated with M3 AML. Poor-risk factors include deletion of 5q and 7q, trisomy 8, t(6; 9), t(9; 22), and a history of myelodysplasia or antecedent hematologic disorder. Patients in the good-risk group have a reasonable chance of cure with intensive postremission therapy, and it may be reasonable to defer transplantation in that group until early first relapse. The poor-risk group is unlikely to be cured with postremission chemotherapy, and allogeneic BMT in CR1 is a reasonable option for patients with an HLA-identical sibling donor. However, even with allogeneic stem cell transplantation, the outcome for patients with high-risk AML is poor (5-year DFS of 8% to 30% for patients with treatment-related leukemia or myelodysplasia). The efficacy of autologous stem cell transplantation in the poor-risk group has not been reported to date but is the subject of active clinical trials. Patients with normal cytogenetics are in an intermediate-risk group, and postremission management should be individualized or, ideally, managed according to a clinical trial.
The rapid engraftment kinetics of peripheral blood progenitor cells demonstrated in trials of high-dose therapy for epithelial neoplasms has led to interest in the alternative use of autologous and allogeneic peripheral blood progenitor cells as rescue for myeloablative therapy for the treatment of AML. One pilot trial of the use of autologous transplantation with unpurged peripheral blood progenitor cells in first remission had a 3-year DFS rate of 35%; detailed prognostic factors for these patients were not provided. This result appears inferior to the best results of chemotherapy or autologous BMT and suggests that the use of peripheral blood progenitor cells be limited to clinical trials.
Allogeneic stem cell transplantation can be performed using stem cells obtained from a bone marrow harvest or a peripheral blood progenitor cell harvest. In a randomized trial of 175 patients undergoing allogeneic stem cell transplantation, with either bone marrow or peripheral blood stem cells, for a variety of hematologic malignancies using methotrexate and cyclosporine to prevent graft-versus-host disease, the use of peripheral blood progenitor cells led to earlier engraftment (median neutrophil engraftment = 16 vs. 21 days, median platelet engraftment = 13 vs. 19 days). The use of peripheral blood progenitor cells was associated with a trend toward increased graft-versus-host disease but comparable transplant-related death. The relapse rate at 2 years appeared lower in patients receiving peripheral blood progenitor cells (hazard ratio [HR], 0.49; 95% confidence interval [CI], 0.24–1.00); however, OS was not significantly increased (HR for death within 2 years, 0.62; 95% confidence interval, 0.38–1.02).Current Clinical Trials
Check for U.S. clinical trials from NCI's list of cancer clinical trials that are now accepting patients with adult 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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