High rate of hematological responses to sorafenib in FLT3-ITD acute myeloid leukemia relapsed after allogeneic hematopoietic stem cell transplantation

Novel Approaches to Treatment of Acute Myeloid Leukemia Relapse Post Allogeneic Stem Cell Transplantation

The management of patients with acute myeloid leukemia (AML) relapsed post allogeneic hematopoietic stem cell transplantation (HSCT) remains a clinical challenge. Intensive treatment approaches are limited by severe toxicities in the early post-transplantation period. Therefore, hypomethylating agents (HMAs) have become the standard therapeutic approach due to favorable tolerability. Moreover, HMAs serve as a backbone for additional anti-leukemic agents. Despite discordant results, the addition of donor lymphocytes infusions (DLI) generally granted improved outcomes with manageable GvHD incidence. The recent introduction of novel targeted drugs in AML gives the opportunity to add a third element to salvage regimens. Those patients harboring targetable mutations might benefit from IDH1/2 inhibitors Ivosidenib and Enasidenib as well as FLT3 inhibitors Sorafenib and Gilteritinib in combination with HMA and DLI. Conversely, patients lacking targetable mutations actually benefit from the addition of Venetoclax. A second HSCT remains a valid option, especially for fit patients and for those who achieve a complete disease response with salvage regimens. Overall, across studies, higher response rates and longer survival were observed in cases of pre-emptive intervention for molecular relapse. Future perspectives currently rely on the development of adoptive immunotherapeutic strategies mainly represented by CAR-T cells.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

FLT3-inhibitor therapy for prevention and treatment of relapse after allogeneic hematopoietic cell transplantation

The curative potential of allogeneic hematopoietic cell transplantation (allo-HCT) for acute myeloid leukemia (AML) relies on the graft-versus-leukemia (GVL)-effect. Relapse after allo-HCT occurs in a considerable proportion of patients, and has a dismal prognosis with very limited curative potential, especially for patients with FLT-ITD-mutated AML. Since the first description of sorafenib for treatment of FLT3-ITD-mutated AML, several clinical trials have tried to determine the efficacy of FLT3 inhibitors for preventing and treating AML relapse after allo-HSCT, but many questions regarding differences among compounds and mechanisms of action remain unanswered. This review provides an overview on the established and evolving use of FLT3 inhibitors to prevent or treat relapse of AML in the context of allo-HCT, focusing on the recently discovered immunogenic potential of some FLT3 inhibitors and addressing the possible mechanisms of leukemia drug-escape.

The added value of multi-state modelling in a randomized controlled trial: The HOVON 102 study re-analyzed

Clofarabine is an active antileukemic drug for subgroups of patients with acute myeloid leukemia (AML). Multi-state models can provide additional insights to supplement the original intention-to-treat analysis of randomized controlled trials (RCT). We re-analyzed the HOVON102/SAKK30/09 phase III RCT for newly diagnosed AML patients, which randomized between standard induction chemotherapy with or without clofarabine. Using multi-state models, we evaluated the effects of induction chemotherapy outcomes (complete remission [CR], measurable residual disease [MRD]), and post-remission therapy with allogeneic stem cell transplantation [alloSCT] on relapse and death. Through the latter a consistent reduction in the hazard of relapse in the clofarabine arm compared to the standard arm was found, which occurred irrespective of MRD status or post-remission treatment with alloSCT, demonstrating a strong and persistent antileukemic effect of clofarabine. During the time period between achieving CR and possible post-remission treatment with alloSCT, non-relapse mortality was higher in patients receiving clofarabine. An overall net benefit of treatment with clofarabine was identified using the composite endpoint current leukemia-free survival (CLFS). In conclusion, these results enforce and extend the earlier reported beneficial effect of clofarabine in AML and show that multi-state models further detail the effect of treatment on competing and series of events.

FLT3 Mutations in Acute Myeloid Leukemia: Key Concepts and Emerging Controversies

The FLT3 receptor is overexpressed on the majority of acute myeloid leukemia (AML) blasts. Mutations in FLT3 are the most common genetic alteration in AML, identified in approximately one third of newly diagnosed patients. FLT3 internal tandem duplication mutations (FLT3-ITD) are associated with increased relapse and inferior overall survival. Multiple small molecule inhibitors of FLT3 signaling have been identified, two of which (midostaurin and gilteritinib) are currently approved in the United States, and many more of which are in clinical trials. Despite significant advances, resistance to FLT3 inhibitors through secondary FLT3 mutations, upregulation of parallel pathways, and extracellular signaling remains an ongoing challenge. Novel therapeutic strategies to overcome resistance, including combining FLT3 inhibitors with other antileukemic agents, development of new FLT3 inhibitors, and FLT3-directed immunotherapy are in active clinical development. Multiple questions regarding FLT3-mutated AML remain. In this review, we highlight several of the current most intriguing controversies in the field including the role of FLT3 inhibitors in maintenance therapy, the role of hematopoietic cell transplantation in FLT3-mutated AML, use of FLT3 inhibitors in FLT3 wild-type disease, significance of non-canonical FLT3 mutations, and finally, emerging concerns regarding clonal evolution.

Effect of the Thiotepa Dose in the TBF Conditioning Regimen in Patients Undergoing Allogeneic Stem Cell Transplantation for Acute Myeloid Leukemia in Complete Remission: A Report From the EBMT Acute Leukemia Working Party

BACKGROUND

Allogeneic stem cell transplantation is a potentially curative therapy for patients with acute myeloid leukemia (AML) after achieving complete remission (CR). The aim of this study is to evaluate the optimal dose of thiotepa, administered as part of the thiotepa-busulfan-fludarabine (TBF) conditioning regimen for allogeneic stem cell transplantation in adults with AML in CR.

PATIENTS AND METHODS

In a retrospective multicenter analysis, we identified 240 patients allotransplanted from matched related or unrelated donors or T replete haplo-identical donors. We compared the transplantation outcomes of patients who received 5 mg/kg thiotepa and 2 days of intravenous busulfan at 6.4 mg/kg (T1B2F) versus those who received 10 mg/kg thiotepa with 2 days of intravenous busulfan at 6.4 mg/kg (T2B2F). The median follow-up was 20 months.

RESULTS

On univariate analysis, the incidence of acute graft versus host disease (GVHD) grade II to IV was significantly lower in the T1B2F group (19%) versus 32% in the T2B2F group (P = .029). This result was confirmed on multivariate analysis; acute GVHD was higher for patients receiving T2B2F (hazard ratio, 2.22; P = .024). No significant change in non-relapse mortality, progression-free survival, or overall survival was observed between the 2 groups.

CONCLUSION

T2B2F is associated with a higher incidence of acute GVHD compared with T1B2F. These results suggest that a lower dose-intensity of thiotepa and busulfan in the TBF regimen may yield better results in patients with AML in CR.

Immunological and Clinical Impact of Manipulated and Unmanipulated DLI after Allogeneic Stem Cell Transplantation of AML Patients

Allogeneic stem cell transplantation (allo-SCT) is the preferred curative treatment for several hematological malignancies. The efficacy of allo-SCT depends on the graft-versus-leukemia (GvL) effect. However, the prognosis of patients with relapsed acute myeloid leukemia (AML) following allo-SCT is poor. Donor lymphocyte infusion (DLI) is utilized after allo-SCT in this setting to prevent relapse, to prolong progression free survival, to establish full donor chimerism and to restore the GvL effect in patients with hematological malignancies. Thus, there are different options for the administration of DLI in AML patients. DLI is currently used prophylactically and in the setting of an overt relapse. In addition, in the minimal residual disease (MRD) setting, DLI may be a possibility to improve overall survival. However, DLI might increase the risk of severe life-threatening complications such as graft-versus-host disease (GvHD) as well as severe infections. The transfusion of lymphocytes has been tested not only for the treatment of hematological malignancies but also chronic infections. In this context, manipulated DLI in a prophylactic or therapeutic approach are an option, e.g., virus-specific DLI using different selection methods or antigen-specific DLI such as peptide-specific CD8+ cytotoxic T lymphocytes (CTLs). In addition, T cells are also genetically engineered, using both chimeric antigen receptor (CAR) genetically modified T cells and T cell receptor (TCR) genetically modified T cells. T cell therapies in general have the potential to enhance antitumor immunity, augment vaccine efficacy, and limit graft-versus-host disease after allo-SCT. The focus of this review is to discuss the different strategies to use donor lymphocytes after allo-SCT. Our objective is to give an insight into the functional effects of DLI on immunogenic antigen recognition for a better understanding of the mechanisms of DLI. To ultimately increase the GvL potency without raising the risk of GvHD at the same time.

The Graft-Versus-Leukemia Effect in AML

Allogeneic hematopoietic stem cell transplantation (allo-SCT) is the most established and commonly used cellular immunotherapy in cancer care. It is the most potent anti-leukemic therapy in patients with acute myeloid leukemia (AML) and is routinely used with curative intent in patients with intermediate and poor risk disease. Donor T cells, and possibly other immune cells, eliminate residual leukemia cells after prior (radio)chemotherapy. This immune-mediated response is known as graft-versus-leukemia (GvL). Donor alloimmune responses can also be directed against healthy tissues, which is known as graft-versus-host disease (GvHD). GvHD and GvL often co-occur and, therefore, a major barrier to exploiting the full immunotherapeutic benefit of donor immune cells against patient leukemia is the immunosuppression required to treat GvHD. However, curative responses to allo-SCT and GvHD do not always occur together, suggesting that these two immune responses could be de-coupled in some patients. To make further progress in successfully promoting GvL without GvHD, we must transform our limited understanding of the cellular and molecular basis of GvL and GvHD. Specifically, in most patients we do not understand the antigenic basis of immune responses in GvL and GvHD. Identification of antigens important for GvL but not GvHD, and vice versa, could impact on donor selection, allow us to track GvL immune responses and begin to specifically harness and strengthen anti-leukemic immune responses against patient AML cells, whilst minimizing the toxicity of GvHD.

Leukemia relapse following unmanipulated haploidentical transplantation: a risk factor analysis on behalf of the ALWP of the EBMT

BACKGROUND

As information on incidence, risk factors, and outcome of acute leukemia (AL) relapse after unmanipulated haploidentical stem cell transplantation (haplo-SCT) is scarce, a retrospective registry study was performed by the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation.

METHODS

Among 1652 transplants performed for lymphoblastic and myeloid AL between 2007 and 2014, 587 patients (acute lymphoblastic leukemia (ALL) 131, acute myeloid leukemia (AML) 456) with detailed information were analyzed aiming to identify risk factors for post-transplant relapse and for overall survival (OS) after relapse.

RESULTS

The cumulative incidence of relapse at 3 years was 44% (35-53%) for ALL and 32% (27-36%) for AML (p = 0.023). In ALL, risk factors for relapse were disease status different from the first complete remission (CR1) at haplo-SCT (CR2 vs CR1: HR 2.85, p = 0.011; advanced vs CR1: HR 14.28, p < 0.0001) and male donor gender (HR 3.64, p = 0.0002), while in AML, risk factors were advanced disease at haplo-SCT (advanced vs CR1: HR 3.95, p < 0.0001) and comorbidities (HCT-CI) ≥ 3 (HR 1.75, p = 0.014). Transplants performed in more recent years were associated with lower relapse incidence (RI) in AML, but not in ALL (HR 0.91, p = 0.042). After relapse, median follow-up was 13 months (mos). OS at 1-year post relapse was 18%. Prognostic factors for superior OS after relapse were remission at time of haplo-SCT (CR vs advanced: HR 0.71, p = 0.028), time from transplant to relapse (≥ 5 mos vs < 5 mos: HR 0.530, p < 0.0001), and bone marrow as a stem cell source (peripheral blood (PB) vs bone marrow (BM): HR 1.473, p = 0.016).

CONCLUSIONS

Risk factors for relapse after haploidentical transplantation were disease specific. Longer OS after relapse was achieved in particular by patients both in CR at haplo-SCT and relapsing more than 5 months after transplant (1-year OS 33%).

Novel treatments for relapsed/refractory acute myeloid leukemia with FLT3 mutations

Introduction: Mutations in the gene encoding for the FMS-like tyrosine kinase 3 (FLT3) are present in about 30% of adults with AML and are associated with shorter disease-free and overall survival after initial therapy. Prognosis of relapsed/refractory AML with FLT3 mutations is even more dismal with median overall survival of a few months only. Areas covered: This review will cover current and emerging treatments for relapsed/refractory AML with FLT3 mutations, preclinical rationale and clinical trials with new encouraging data for this particularly challenging population. The authors discuss mechanisms of resistance to FLT3 inhibitors and how these insights serve to identify current and future treatments. As allogeneic stem cell transplant in the first remission is the preferred therapy for newly diagnosed AML patients with FLT3 mutations, the authors discuss the role of maintenance after SCT for the prevention of relapse. Expert opinion: Relapsed/refractory AML with FLT3 mutations remains a therapeutic challenge with currently available treatments. However, the evolution of targeted therapies with next-generation FLT3 inhibitors and their combinations with chemotherapy is showing much promise. Moreover, growing understanding of the pathways of resistance to treatment has led to the identification of various targeted therapies currently being explored, which in time will improve outcomes.

Sorafenib Therapy Is Associated with Improved Outcomes for FMS-like Tyrosine Kinase 3 Internal Tandem Duplication Acute Myeloid Leukemia Relapsing after Allogeneic Hematopoietic Stem Cell Transplantation

The optimal therapy for patients with acute myeloid leukemia (AML) with FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) who relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains unclear. In this study we retrospectively evaluated the efficacy of sorafenib combined with other therapeutic strategies as salvage therapy for these patients. Eighty-three AML patients with FLT3-ITD relapsing after allo-HSCT were enrolled in this study. Fifty-three patients received salvage therapy containing sorafenib and 30 patients did not. Salvage therapy containing sorafenib was superior to that without sorafenib with respect to complete remission rates, overall survival (OS), and progression-free survival (PFS) (66.0% versus 30.0%, 46.8% versus 20.0%, and 44.9% versus 16.7%, respectively; P = .002, P = .003, and P = .001). Further subgroup analysis revealed that the OS and PFS of patients who received sorafenib combined with chemotherapy followed by donor lymphocyte infusion (DLI) were superior to those receiving other therapeutic regimens, including sorafenib combined with chemotherapy, chemotherapy followed by DLI, and monochemotherapy (P = .003, P < .001). Multivariate analysis revealed that salvage therapy including sorafenib was the only protective factor for longer OS (P = .035; hazard ratio [HR], .526); salvage therapy including sorafenib and DLI were the protective factors for longer PFS (P = .011, HR, .423; P = .019, HR, .508). Our data suggest that sorafenib therapy is associated with improved outcomes for FLT3-ITD AML relapsing after allo-HSCT, and whether sorafenib combined with chemotherapy followed by DLI reveals an optimal efficacy merits further study.

Mechanisms of immune escape after allogeneic hematopoietic cell transplantation

Relapse of the original disease is a major cause of death after allogeneic hematopoietic cell transplantation for acute leukemias. There is growing evidence that relapses may be explained not only by resistance to chemotherapy but also by the escape of tumor cells from the control of the allogeneic immune response. Mechanisms of immune evasion can involve abrogation of leukemia cell recognition due to loss of HLA genes, immunosuppression by immune-checkpoint ligand expression, production of anti-inflammatory factors, release of metabolically active enzymes, loss of proinflammatory cytokine production, and acquisition of novel driver mutations that promote leukemia outgrowth. These mechanisms, and therapeutic targeting of immune escape, will be discussed. We divide the evidence in support of immune-escape mechanisms into animal studies, human laboratory studies, and human clinical experience. A better understanding of the molecular pathways connected to immune escape and relapse may help to improve our therapeutic armamentarium against acute myeloid leukemia relapse.

[Second allogeneic hematopoietic stem cell transplant: Guidelines from the francophone Society of bone marrow transplantation and cellular therapy (SFGM-TC)]

Disease recurrence and graft dysfunction after allogeneic hematopoietic stem cell transplantation (allo-HSCT) currently remain among the major causes of treatment failure in malignant and non-malignant hematological diseases. A second allo-HSCT is a valuable therapeutic option to salvage those situations. During the 8th annual harmonization workshops of the french Society of bone marrow transplantation and cellular therapy (SFGM-TC), a designated working group reviewed the literature in order to elaborate unified guidelines on feasibility, indications, donor choice and conditioning in the case of a second allo-HSCT. In case of relapse, a second allo-HSCT with reduced intensity or non-myeloablative conditioning is a reasonable option, particularly in patients with a good performance status (Karnofsky/Lansky>80%), low co-morbidity score (EBMT score≤3), a longer remission duration after the first allo-HSCT (>6 months), and who present low disease burden at the time of second allo-HSCT. Matched related donors tend to be associated with better outcomes. In the presence of graft dysfunction (primary and secondary graft rejection), an immunoablative conditioning regimen is recommended. A donor change remains a valid option, especially in the absence of graft-versus-host disease after the first allo-HSCT.

Sorafenib Combined with 5-azacytidine in Older Patients with Untreated FLT3-ITD Mutated Acute Myeloid Leukemia

Based on our previous study of the combination of sorafenib with 5-azacytidine (AZA) in relapsed/refractory patients with FLT3 mutated acute myeloid leukemia (AML), we hypothesized that the combination would be efficacious and well tolerated in untreated patients with FLT3 mutated AML who are unsuitable for standard chemotherapy due to advanced age or lack of fitness. Newly diagnosed patients with untreated FLT3 mutated AML who underwent frontline therapy on 2 separate protocols of AZA plus sorafenib were analyzed. The clinical trials were registered at clinicaltrials.gov (NCT02196857 and NCT01254890). Overall, 27 patients with untreated FLT3 mutated AML (median age of 74 years, range, 61-86) were enrolled. The overall response rate was 78% (7 [26%] CR, 12 [44%] CRi/CRp, and 2 [7%] PR). Patients received a median of 3 treatment cycles (1-35). The median duration of CR/CRp/CRi is 14.5 months (1.1-28.7 months). Three (11%) responding patients (1 CR, 2 CRi) proceeded to allogeneic stem cell transplant. The median follow-up for surviving patients was 4.1 months (3.0-17.3 months). The median overall survival for the entire group was 8.3 months, and 9.2 months in the 19 responders. The regimen was well tolerated in elderly patients with untreated FLT3 mutated AML with no early deaths.

[Outcome of acute myeloid leukemia with FLT3-ITD mutation treated by allogeneic hematopoietic stem cell transplantation]

Objective: To evaluate the efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for the treatment of acute myeloid leukemia (AML) patients with FLT3-ITD mutation. Methods: From September 2008 to December 2016, 40 AML patients with FLT3-ITD mutation were enrolled in the study. The therapeutic process, outcomes and prognostic factors were retrospectively analyzed. Results: The median of WBC at initial diagnosis was 35.0 (range 1.7-185.0) ×10(9)/L. The median course number of chemotherapy was 4 (range 2-7). At the time of transplantation, 34 patients were at the first complete remission (CR(1)) stage, and the other 6 ones were non-remission after chemotherapy. 24 patients received allogeneic transplants from an HLA-matched sibling donor, 7 cases from a HLA-matched unrelated donor, the remaining 9 ones received allograft from a haploidentical donor. The rate of 3-year overall survival (OS) and disease free survival (DFS) in all patients were both 74.3% (95% CI 60.4%-88.2%). The 3-year cumulative incidences of disease relapse and non-relapse mortality were 7.5% (95%CI 1.9%-18.4%) and 18.2% (95% CI 7.9%-32.0%), respectively. More than one course of chemotherapy before achieving CR(1) and the occurrence of acute GVHD after transplantation were associated with poor outcome in terms of OS and DFS. The relapse rates were significantly lower in patients receiving transplantation at CR(1) stage [0 vs 50.0% (95%CI 77.7%-82.9%) , P<0.001] and achieving CR(1) after one course induction therapy [0 vs 16.7% (95%CI 3.9%-37.3%) , P=0.020]. Conclusions: Allo-HSCT was an efficient approach for AML patients with FLT3-ITD mutation. Patients obtained better survival, especially for those achieving CR after one course induction therapy and receiving transplantation at CR(1) stage.

Effect of sorafenib on the outcomes of patients with FLT3-ITD acute myeloid leukemia undergoing allogeneic hematopoietic stem cell transplantation

BACKGROUND

The objective of this study was to evaluate the effect of sorafenib on the outcomes of patients with acute myeloid leukemia (AML) with FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT).

METHODS

A total of 144 patients with FLT3-ITD AML undergoing allo-HSCT between January 2012 and December 2015 were enrolled in this study. Depending on whether they were receiving sorafenib before transplantation or sorafenib maintenance after transplantation, patients were divided into 4 groups: patients receiving sorafenib before transplantation (group A; n = 36), patients receiving sorafenib after transplantation (group B; n = 32), patients receiving sorafenib both before and after transplantation (group C; n = 26), and patients receiving sorafenib neither before nor after transplantation (group D; n = 50). Outcomes were compared among these groups.

RESULTS

The 3-year relapse rates were 22.2%, 18.8%, 15.8%, and 46.1% for groups A, B, C, and D, respectively (P = .006). The 3-year overall survival (OS) rates were 74.9%, 78.1%, 84.6%, and 50.9%, respectively (P = .023), and the 3-year leukemia-free survival (LFS) rates were 69.4%, 78.1%, 80.4%, and 34.8%, respectively (P < .001). The relapse rate was higher and the LFS was shorter in group D versus groups A, B, and C. The OS in group D was shorter than the OS in group C but was similar to the OS in groups A and B. A multivariate analysis revealed that sorafenib before transplantation, sorafenib maintenance after transplantation, and their combined application were protective factors for a lower relapse rate (hazard ratios [HRs], 0.436 [P = .048], 0.431 [P = .046], and 0.173 [P = .002], respectively) and longer LFS (HRs, 0.322 [P = .010], 0.343 [P = .014], and 0.187 [P = .001], respectively).

CONCLUSIONS

Sorafenib before transplantation, sorafenib maintenance after transplantation, and their combined application all could improve the outcomes for patients with FLT3-ITD AML. Further study is needed to determine whether the use of sorafenib both before and after transplantation might be ideal. Cancer 2018;124:1954-63. © 2018 American Cancer Society.

[Preventative and therapeutic relapse strategies after allogeneic hematopoietic stem cell transplantation: Guidelines from the Francophone society of bone marrow transplantation and cellular therapy (SFGM-TC)]

Disease relapse remains the first cause of mortality of hematological malignancies after allogeneic hematopoietic stem cell transplantation (allo-HCT). The risk of recurrence is elevated in patients with high-risk cytogenetic or molecular abnormalities, as well as when allo-HCT is performed in patients with refractory disease or with persistent molecular or radiological (PET-CT scan) residual disease. Within the frame of the 7th annual workshops of the francophone society for bone marrow transplantation and cellular therapy, the working group reviewed the literature in order to elaborate unified guidelines for the prevention and treatment of relapse after allo-HCT. For high risk AML and MDS, a post transplant maintenance strategy is possible, using hypomethylating agents or TKI anti-FLT3 when the target is present. For Philadelphia positive ALL, there was a consensus for the use of post-transplant TKI maintenance. For lymphomas, there are no strong data on the use of post-transplant maintenance, and hence a preemptive strategy is recommended based on modulation of immunosuppression, close follow-up of donor chimerism, and donor lymphocytes infusion. For multiple myeloma, even though the indication of allo-HCT is controversial, our recommendation is post transplant maintenance using bortezomib, due to its a good toxicity profile without increasing the risk of GVHD.

Treatment of Acute Myeloid Leukemia with the FLT3 Gene Mutation

In acute myeloid leukemia (AML), mutations of the Fms-like tyrosine kinase 3 receptor (FLT3) and its overexpression are related with hyperleukocytosis, higher risk of relapse, and decrease of both disease-free survival and overall survival. It has been suggested that this phenomenon confers proliferative and survival advantages to the malignant blast cells. As a consequence, it is an attractive therapeutic target. As the best treatment strategy for mutated FLT3 AML remains to be defined, the addition of FLT3 inhibitor drugs to chemotherapy or to the bone marrow transplant approach has become a growing strategy. With encouraging results, this combination seems to be an attractive option. Relevant data regarding the current treatment trends on mutated FLT3 AML is reviewed here.

FLT3 inhibitors: clinical potential in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive hematopoietic malignancy that is cured in as few as 15%–40% of cases. Tremendous improvements in AML prognostication arose from a comprehensive analysis of leukemia cell genomes. Among normal karyotype AML cases, mutations in the FLT3 gene are the ones most commonly detected as having a deleterious prognostic impact. FLT3 is a transmembrane tyrosine kinase receptor, and alterations of the FLT3 gene such as internal tandem duplications (FLT3-ITD) deregulate FLT3 downstream signaling pathways in favor of increased cell proliferation and survival. FLT3 tyrosine kinase inhibitors (TKI) emerged as a new therapeutic option in FLT3-ITD AML, and clinical trials are ongoing with a variety of TKI either alone, combined with chemotherapy, or even as maintenance after allogenic stem cell transplantation. However, a wide range of molecular resistance mechanisms are activated upon TKI therapy, thus limiting their clinical impact. Massive research efforts are now ongoing to develop more efficient FLT3 TKI and/or new therapies targeting these resistance mechanisms to improve the prognosis of FLT3-ITD AML patients in the future.

Inhibition of FLT3 in AML: a focus on sorafenib

FMS-like tyrosine kinase 3 (FLT3) is one of the most commonly mutated genes in AML. FLT3 is mutated in ~30% of patients with AML, either by internal tandem duplications (FLT3-ITD) of the juxta-membrane domain or by a point mutation, usually involving the tyrosine kinase domain. Several FLT3 tyrosine kinase inhibitors are being evaluated in multiple studies aiming at improving outcomes. The most widely used is sorafenib, a potent multikinase inhibitor approved for hepatocellular carcinoma and renal cell carcinoma. Sorafenib monotherapy or in combination with conventional chemotherapy, has been evaluated in various settings in AML, including front-line, relapsed or refractory disease including post-allograft failures and, more recently, as post-transplant maintenance therapy. Encouraging data have emerged with several other agents like lestaurtinib, midostaurin, crenolanib, gilteritinib and quizartinib. Although transient responses to FLT3 inhibitors are often observed in case of disease relapse, the most promising approach is the use of FLT3 inhibitors either in combination with induction chemotherapy or as consolidation/maintenance therapy after allogeneic hematopoietic cell transplantation. In this review, we summarize the clinical data on sorafenib and other FLT3 inhibitors in AML.

Predictive significance of the European LeukemiaNet classification of genetic aberrations in patients with acute myeloid leukaemia undergoing allogeneic stem cell transplantation

OBJECTIVES

The purpose of this study was to evaluate the predictive capacity of the European LeukemiaNet (ELN) classification of genetic risk in patients with acute myeloid leukaemia (AML) undergoing allogeneic stem cell transplantation (alloSCT).

METHODS

We retrospectively analysed 274 patients transplanted at our centre between 2004 and 2014.

RESULTS

The ELN grouping is comparable to the Southwest Oncology Group/Eastern Cooperative Oncology Group (SWOG/ECOG) stratification in predicting the outcome after alloSCT [overall P = 0.0064 for disease-free survival (DFS), overall P = 0.003 for relapse]. Patients with an intermediate-1 profile have a significantly elevated 5-yr relapse incidence as compared to favourable risk patients, that is 40% vs. 15%, [hazard ratio (HR) 2.58, P = 0.048]. An intermediate-1 risk profile is an independent predictor for relapse as determined by multivariate Cox regression analysis (HR 3.05, P = 0.023). In intermediate-1 patients, the presence of an FLT3 internal tandem duplication (FLT3-ITD) is associated with a significantly increased relapse incidence (P = 0.0323), and a lower DFS (P = 0.0465). FLT3-ITD is an independent predictor for overall survival, DFS and relapse incidence in the intermediate-1 subgroup.

CONCLUSIONS

The ELN stratification of genetic risk predicts the outcome of patients with AML undergoing alloSCT. Patients with an intermediate-1 profile have a high risk for treatment failure due to relapse, which prompts the development of alternative treatment strategies.

Pharmacologic maintenance strategies following allogeneic hematopoietic cell transplantation for acute myeloid leukemia

The use of pharmacologic agents to maintain remission following allogeneic hematopoietic cell transplantation (HCT) is a topic of increasing interest and exploration for patients with high-risk acute myeloid leukemia (AML). This review details published and ongoing studies focused on post-transplant pharmacologic maintenance for AML. While early phase studies have demonstrated the safety and tolerability of various maintenance approaches following HCT, the results of several ongoing randomized prospective studies will be required to determine the clinical efficacy needed to expand this approach from experimental to standard of care.