Timing of allogeneic hematopoietic cell transplantation (alloHCT) for chronic myeloid leukemia (CML) patients

The Role of Molecular or Cytogenetic Response as a Favorable Prognostic Factor Before Hematopoietic Stem Cell Transplantation for Chronic Myeloid Leukemia

Tyrosine kinase inhibitors (TKIs) have revolutionized therapy for patients with chronic myeloid leukemia (CML) over the last two decades. However, some patients still do not achieve an adequate response to these drugs, and hematopoietic stem cell transplantation (HSCT) is indicated in this scenario. We present the results of a 20-year follow-up study of 70 patients who underwent transplantation after TKI failure. The primary objective of this study was to evaluate overall survival (OS) and the secondary objective was to evaluate the outcomes of relapse-free survival (RFS), GVHD-free, relapse-free survival (GFRS) and the incidences of relapse (RI), non-relapse mortality (NRM), acute and chronic GVHD. Median survival was 11 years, with a 1-year OS of 70% (57.8 to 79.3) and a 5-year OS of 57.7% (45.1 to 68.5). The estimated 5-year OS was not different for CP1 (60%) versus advanced stages (45%); P = .60. The degree of response immediately before transplantation was directly associated with worse outcomes [HR 5.89 (1.19-29.16); P = .03] for patients with only a hematological response compared with patients with a cytogenetic or molecular response. This study corroborates the potential of HSCT in the scenario of therapeutic failure and highlights the role of molecular or cytogenetic response as a potential target to be achieved before transplantation.

An Update on the Management of Advanced Phase Chronic Myeloid Leukemia

PURPOSE OF REVIEW

While most patients with chronic myeloid leukemia (CML) present in a chronic phase and are expected to have a normal life expectancy, some patients present with or progress to a more aggressive accelerated phase (AP) or blast phase (BP) of CML. Herein, we discuss the diagnostic considerations of advanced phase CML and review its contemporary management.

RECENT FINDINGS

Later-generation, more potent BCR::ABL1 tyrosine kinase inhibitors (TKIs) such as ponatinib may result in superior outcomes in patients with advanced phase CML. For CML-BP, combination approaches directed against the blast immunophenotype appear superior to TKI monotherapy. The role of allogeneic stem cell transplantation is controversial in CML-AP but has consistently been shown to improve outcomes for patients with CML-BP. Advanced phase CML, particularly CML-BP, remains a poor risk subtype of CML. However, novel combination approaches using later-generation TKIs are being explored in clinical trials and may lead to improved outcomes.

Pathogenesis and management of accelerated and blast phases of chronic myeloid leukemia

The treatment of chronic myeloid leukemia (CML) with tyrosine kinase inhibitors (TKIs) has been a model for cancer therapy development. Though most patients with CML have a normal quality and duration of life with TKI therapy, some patients progress to accelerated phase (AP) and blast phase (BP), both of which have a relatively poor prognosis. The rates of progression have reduced significantly from over >20% in the pre-TKI era to <5% now, largely due to refinements in CML therapy and response monitoring. Significant insights have been gained into the mechanisms of disease transformation including the role of additional cytogenetic abnormalities, somatic mutations, and other genomic alterations present at diagnosis or evolving on therapy. This knowledge is helping to optimize TKI therapy, improve prognostication and inform the development of novel combination regimens in these patients. While patients with de novo CML-AP have outcomes almost similar to CML in chronic phase (CP), those transformed from previously treated CML-CP should receive second- or third- generation TKIs and be strongly considered for allogeneic stem cell transplantation (allo-SCT). Similarly, patients with transformed CML-BP have particularly dismal outcomes with a median survival usually less than one year. Combination regimens with a potent TKI such as ponatinib followed by allo-SCT can achieve long-term survival in some transformed BP patients. Regimens including venetoclax in myeloid BP or inotuzumab ozogamicin or blinatumomab in lymphoid BP might lead to deeper and longer responses, facilitating potentially curative allo-SCT for patients with CML-BP once CP is achieved. Newer agents and novel combination therapies are further expanding the therapeutic arsenal in advanced phase CML.

Transplantation in CML in the TKI era: who, when, and how?

Molecular therapy with tyrosine kinase inhibitors (TKIs) has significantly reduced the indication for allogeneic hematopoietic stem cell transplantation (allo-HSCT) in chronic myeloid leukemia (CML). Treatment-free remission can be obtained in about 50% of patients with an optimal response. However, cure rates up to 90% are restricted to patients receiving HSCT. Timing is essential since HSCT in the early stages of the disease has the best outcome. Patients in a more advanced phase (AdP) than chronic-phase (chP) CML undergo HSCT with suboptimal outcomes, and the gap between chP and AdP disease is widening. First-line therapy should start with first- or second-generation (G) TKIs. Patients failing treatment (BCR-ABL1 transcripts of greater than 10% at 3 and 6 months and greater than 1% at 12 months) should be switched to second-line TKIs, and HSCT should be considered. Patients not responding to 2G-TKI therapy as well as patients in an accelerated phase (AP) or blast crisis (BC) are candidates for HSCT. Therapy resistant BCR-ABL1 mutations, high-risk additional cytogenetic abnormalities, and molecular signs of leukemia progression should trigger the indication for HSCT. Patients who, despite dose adjustments, do not tolerate or develop severe adverse events, including vascular events, to multiple TKIs are also candidates for HSCT. In AdP CML, TKIs do not show long-lasting results, and the outcome of HSCT is less optimal without pretransplant therapy. In these patients the induction of chP2 with TKIs, either alone (AP) or in combination with intensive chemotherapy (BC), followed by HSCT should be pursued.

Questions concerning tyrosine kinase-inhibitor therapy and transplants in chronic phase chronic myeloid leukaemia

In this provocative commentary, we consider several questions posed by the late chronic myeloid leukaemia (CML) expert Prof. Michele Baccarani, which he challenged us to address after his death. He noted only a small proportion of people with chronic phase CML receiving tyrosine kinase-inhibitor (TKI)-therapy are likely to achieve sustained therapy-free remission (TFR) and even fewer are likely to be cured. Persons most likely to fail TKItherapy can be identified at diagnosis or soon after starting TKI-therapy. These persons are likely to need lifetime TKI-therapy with attendant risks of adverse events, cost and psychological consequences. Allogeneic transplants achieve much higher rates of leukaemia-free survival compared with TKI-therapy but are associated with transplant-related adverse events including an almost 20 percent risk of transplant-related deaths within 1 year post-transplant and a compromised quality-of-life because of complications such as chronic graft-versus-host disease. Subject-, disease- and transplant-related co-variates associated with transplant outcomes are known with reasonable accuracy. Not everyone likely to fail TKI-therapy is a transplant candidate. However, in those who candidates are physicians and patients need to weigh benefits and risks of TKI-therapy versus a transplant. We suggest transplants should be more often considered in the metric when counseling people with chronic phase CML unlikely to achieve TFR with TKI-therapy. We question whether we are discounting a possible important therapy intervention; we think so.

Ponatinib for the treatment of adult patients with resistant or intolerant Chronic-Phase Chronic Myeloid Leukemia

INTRODUCTION

Patients with chronic myeloid leukemia in chronic phase (CP-CML) who are resistant or intolerant to second-generation tyrosine kinase inhibitors (TKIs) may benefit from treatment with a third-generation TKI, like ponatinib.

AREAS COVERED

In this review, the authors discuss the role of ponatinib, an oral pan-inhibitor of BCR-ABL1, with potent activity in heavily pretreated patients, including T315I mutation. In the long-term follow-up of the PACE trial, 60% of patients with prior TKIs exposure achieved a major cytogenetic response with ponatinib and 40% a major molecular response; 5-year overall survival was 73%. Cardiovascular adverse events represent the major toxicity associated with ponatinib. Adopting a dose-reduction approach appeared to be safe: starting with 45 or 30 mg and decreasing to 15 mg once BCR-ABL1/ABL1≤1% is achieved. In patients who are not candidates for ponatinib therapy, asciminib or other novel TKIs like HQP1351, represent alternative options.

EXPERT OPINION

In patients with CP-CML resistant or intolerant to second-generation TKIs, we favor using a third-generation TKI such as ponatinib. Although we initiate a donor search as soon as a patient fails a second-generation TKI, we still prefer treating patients with ponatinib and will only consider transplantation in the event of no response or disease progression.