Clinical impact of pretransplant use of multiple tyrosine kinase inhibitors on the outcome of allogeneic hematopoietic stem cell transplantation for chronic myelogenous leukemia

Therapeutic options for chronic myeloid leukemia following the failure of second-generation tyrosine kinase inhibitor therapy

The management of chronic myeloid leukemia in the chronic phase (CML-CP) has witnessed significant advancements since the identification of a common chromosomal translocation anomaly involving chromosomes 9 and 22, which results in the formation of the Philadelphia chromosome driven by the BCR-ABL1 fusion protein. This discovery paved the way for the development of tyrosine kinase inhibitors (TKIs) that target the adenosine triphosphate (ATP) binding site of ABL1 through the BCR-ABL-1 fusion protein. Following the approval of Imatinib by the Food and Drug Administration (FDA) as the first TKI for CML treatment in 2001, the median overall survival (OS) for chronic phase CML (CML-CP) has significantly improved, approaching that of the general population. However, achieving this milestone crucially depends on reaching certain treatment response milestones. Since the introduction of imatinib, five additional TKIs have been approved for CML-CP treatment. Despite the availability of these treatments, many patients may experience treatment failure and require multiple lines of therapy due to factors such as the emergence of resistance, such as mutations in the ATP binding site of ABL, or intolerance to therapy. This review will primarily focus on exploring treatment options for patients who fail second-generation TKI therapy due to true resistance.

Allogeneic hematopoietic cell transplantation in patients with chronic phase chronic myeloid leukemia in the era of third generation tyrosine kinase inhibitors: A retrospective study by the chronic malignancies working party of the EBMT

Following the introduction of tyrosine kinase inhibitors (TKI), the number of patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT) for chronic phase (CP) chronic myeloid leukemia (CML) has dramatically decreased. Imatinib was the first TKI introduced to the clinical arena, predominantly utilized in the first line setting. In cases of insufficient response, resistance, or intolerance, CML patients can subsequently be treated with either a second or third generation TKI. Between 2006 and 2016, we analyzed the impact of the use of 1, 2, or 3 TKI prior to allo-HCT for CP CML in 904 patients. A total of 323-, 371-, and 210 patients had 1, 2, or 3 TKI prior to transplant, respectively; imatinib (n = 778), dasatinib (n = 508), nilotinib (n = 353), bosutinib (n = 12), and ponatinib (n = 44). The majority had imatinib as first TKI (n = 747, 96%). Transplants were performed in CP1, n = 549, CP2, n = 306, and CP3, n = 49. With a median follow-up of 52 months, 5-year OS for the entire population was 64.4% (95% CI 60.9-67.9%), PFS 50% (95% CI 46.3-53.7%), RI 28.7% (95% CI 25.4-32.0%), and NRM 21.3% (95% CI 18.3-24.2%). No difference in OS, PFS, RI, or NRM was evident related to the number of TKI prior to allo-HCT or to the type of TKI (p = ns). Significant factors influencing OS and PFS were > CP1 versus CP1 and Karnofsky performance (KPS) score > 80 versus ≤80, highlighting CP1 patients undergoing allo-HCT have improved survival compared to >CP1 and the importance of careful allo-HCT candidate selection.

The Clinical Significance of BCR-ABL1 Mutations in Patients With Philadelphia Chromosome-Positive Chronic Myeloid Leukemia Who Underwent Allogeneic Hematopoietic Cell Transplantation

The global standard therapy for chronic myeloid leukemia (CML) is tyrosine kinase inhibitors (TKIs). One of the causes of therapeutic resistance to some TKIs corresponds to point mutations in the BCR-ABL1 fusion gene. Allogeneic hematopoietic cell transplantation (HCT) is a treatment option for high-risk CML, including TKI resistance. Although BCR-ABL1 point mutations comprise a major factor in the assessment of the indications for HCT, there is limited evidence for their significance in relation to transplant outcomes. This study aimed to evaluate the profiles and transplant outcomes of BCR-ABL1 mutations in allografted patients with CML. The retrospective study used a nationwide registry data including adult patients with CML who underwent their first HCT between 2006 and 2016. The inclusion criterion was the evaluation of the status of the BCR-ABL1 mutation before HCT. The cohort included 315 patients with a median age of 44 years (range 16-70 years). Point mutations were detected in 152 patients, of which 101 (66%) harbored T315I mutations and 51 harbored mutations other than T315I (non-T315I). With a median follow-up period of 38 months (range 2-114 months), overall survival (OS) at 3 years was worse in the mutation group than in the no-mutation group (53% versus 71%; P = .002), which was validated by multivariate analysis (hazard ratio [HR] = 1.50; 95% confidence interval [CI], 1.0-2.2; P = .038); this difference was remarkable in the chronic phase of CML. OS in the non-T315I group was significantly worse than that in the no-mutation group (HR = 1.69; 95% CI, 1.0-2.8; P = .035). The nationwide study has successfully evaluated the BCR-ABL1 mutational profile and its outcomes in patients with CML who received HCT. The mortality risk was significantly higher in patients with the BCR-ABL1 mutation than in patients without the mutation. These findings would be useful to understand the clinical significance of various BCR-ABL1 mutations in CML and provide insight into the on mid need for treatment strategies for cases of CML with BCR-ABL1 mutations.

Outcomes and toxicity of allogeneic hematopoietic cell transplantation in chronic myeloid leukemia patients previously treated with second-generation tyrosine kinase inhibitors: a prospective non-interventional study from the Chronic Malignancy Working Party of the EBMT

Allogeneic hematopoietic cell transplantation (allo-HCT) remains a treatment option for patients with chronic myeloid leukemia (CML) who fail to respond to tyrosine kinase inhibitors (TKIs). While imatinib seems to have no adverse impact on outcomes after transplant, little is known on the effects of prior use of second-generation TKI (2GTKI). We present the results of a prospective non-interventional study performed by the EBMT on 383 consecutive CML patients previously treated with dasatinib or nilotinib undergoing allo-HCT from 2009 to 2013. The median age was 45 years (18-68). Disease status at transplant was CP1 in 139 patients (38%), AP or >CP1 in 163 (45%), and BC in 59 (16%). The choice of 2GTKI was: 40% dasatinib, 17% nilotinib, and 43% a sequential treatment of dasatinib and nilotinib with or without bosutinib/ponatinib. With a median follow-up of 37 months (1-77), 8% of patients developed either primary or secondary graft failure, 34% acute and 60% chronic GvHD. There were no differences in post-transplant complications between the three different 2GTKI subgroups. Non-relapse mortality was 18% and 24% at 12 months and at 5 years, respectively. Relapse incidence was 36%, overall survival 56% and relapse-free survival 40% at 5 years. No differences in post-transplant outcomes were found between the three different 2GTKI subgroups. This prospective study demonstrates the feasibility of allo-HCT in patients previously treated with 2GTKI with a post-transplant complications rate comparable to that of TKI-naive or imatinib-treated patients.

Tyrosine Kinase Inhibitors and Beyond for Chronic Myeloid Leukemia in Children

Chronic myeloid leukemia (CML) is rare in children but presents a unique challenge as recent drug innovations have turned CML into a chronic disease with implications for treatment into adulthood. With the approval of newer-generation tyrosine kinase inhibitors (TKIs) in addition to imatinib, providers have more options for the treatment of chronic-phase CML (CML-CP) in children. The second-generation TKIs approved for use in children, nilotinib and dasatinib, have higher response rates than first-generation imatinib; however, overall survival rates appear to be the same. Even more options may soon become available with ongoing investigations into the use of bosutinib and ponatinib and other new agents in children. Possible long-term side effects of TKIs, including growth failure, should be carefully acknowledged by the treating provider. Although these known associations may not preclude treatment, providers should be aware of them to guide their management of pediatric patients with CML being treated long term with TKI therapy. Treatment-free remission is a desired goal for pediatric patients and providers alike, but current recommendations are for attempts at achieving this to be restricted to clinical study settings.

Efficacy of allogeneic hematopoietic cell transplantation in patients with chronic phase CML resistant or intolerant to tyrosine kinase inhibitors

Approximately 15-20% of chronic myeloid leukemia (CML) patients fail tyrosine kinase inhibitor (TKI) therapy secondary to resistance or intolerance. In the pre-TKI era, front-line allogeneic hematopoietic cell transplantation (allo-HCT) represented the standard approach for patients with chronic phase-CML (CP-CML) who were deemed fit to tolerate the procedure and had a human leukocyte antigen compatible donor available. Currently, CP-CML patients are eligible for allo-HCT only if they fail more than one TKI and/or are intolerant to the drug. We performed a systematic review/meta-analysis of the available literature to assess the evidence regarding allo-HCT efficacy in CP-CML patients. Data from eligible studies were extracted in relation to benefits (overall survival [OS], progression-free survival, disease-free survival [DFS], complete remission [CR], and molecular response [MR]) and harms (nonrelapse mortality [NRM], relapse, and acute and chronic graft-versus-host disease), and stratified by age into adult and pediatric groups. For adult allo-HCT recipients, the pooled OS, DFS, CR and, MR were 84% [95% confidence interval (CI) 59-99%], 66% (95% CI 59-73%), 56% (95% CI 30-80%), and 88% (95% CI 62-98%), respectively. Pooled NRM and relapse were 20% (95% CI 15-26%) and 19% (95% CI 10-28%), respectively. For the pediatric group, the OS rate was reported in one study and was 91% (95% CI 72-99%). Our results suggest that allo-HCT is an effective treatment for TKI-resistant or TKI-intolerant CP-CML. Post-transplant strategies are still needed to further mitigate the risk of relapse.

Complexity of chronic-phase CML management after failing a second-generation TKI

The treatment landscape of chronic myeloid leukemia (CML) was radically changed with the introduction of imatinib in 2001. With the emergence of treatment failure with imatinib, more specific and potent second- and third-generation tyrosine kinase inhibitors (TKIs) were developed. Currently, 6 TKIs and one protein synthesis inhibitor are available on the market for CML treatment. Despite the availability of these agents, it is not uncommon for some patients to experience treatment failure across several lines of therapy. Sequencing the available treatment options is a challenging task that becomes more complex after patients fail the more potent second- and third-generation TKIs. The ability to successfully salvage such patients is limited. In this paper, we will briefly review the mechanisms of treatment failure in chronic-phase CML (CP-CML) and focus on the complexity of managing patients who fail a second-generation TKI.

How I treat chronic myeloid leukemia in children and adolescents

Evidence-based recommendations have been established for treatment of chronic myeloid leukemia (CML) in adults treated with tyrosine kinase inhibitors (TKIs), but the rarity of this leukemia in children and adolescents makes it challenging to develop similar recommendations in pediatrics. In addition to imatinib, which was approved for pediatric CML in 2003, the second-generation TKIs dasatinib and nilotinib were recently approved for use in children, expanding the therapeutic options and pushing allogeneic stem cell transplantation to a third-line treatment of most pediatric cases. Yet, without sufficient data on efficacy and safety specific to pediatric patients, the selection of a TKI continues to rely on clinical experience in adults. Here, we present 4 case scenarios highlighting common yet challenging issues encountered in the treatment of pediatric CML (suboptimal response, poor treatment adherence, growth retardation, and presentation in advanced phases). Limited experience with very young children, the transition of teenagers to adult medicine, and the goal of achieving treatment-free remission for this rare leukemia are additional significant obstacles that require further clinical investigation through international collaboration.