Classification of accelerated phase chronic myeloid leukemia in the era of the BCR::ABL1 tyrosine kinase inhibitors: A work in progress

Is there really an accelerated phase of chronic myeloid leukaemia at presentation?

Whether there is really a distinct accelerated phase (AP) at diagnosis in chronic myeloid leukaemia (CML) in the context of tyrosine kinase-inhibitor (TKI)-therapy is controversial. We studied 2122 consecutive subjects in chronic phase (CP, n = 1837) or AP (n = 285) at diagnosis classified according to the 2020 European LeukemiaNet (ELN) classification. AP subjects with increased basophils only had similar transformation-free survival (TFS) and survival compared with CP subjects classified as ELTS intermediate-risk. Those with increased blasts only had worse TFS but similar survival compared with CP subjects classified as ELTS high-risk. AP subjects with decreased platelets only had similar TFS but worse survival compared with subjects classified as ELTS high-risk. Proportions of CP and AP subjects meeting the 2020 ELN TKI-response milestones were similar. However, worse TFS at 3-month and survival at 6- or 12-month were only in AP subjects failing to meet ELN milestones. Findings were similar using the 2022 International Consensus Classification (ICC) criteria for AP replacing decreased platelets with additional cytogenetic abnormalities. Our data support the 2022 WHO classification of CML eliminating AP. We suggest adding a very high-risk cohort to the ELTS score including people with increased blasts or decreased platelets and dividing CML into 2 phases at diagnosis: CP and acute or blast phases.

Chronic myeloid leukemia: 2025 update on diagnosis, therapy, and monitoring

DISEASE OVERVIEW

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm with an annual incidence of two cases/100 000. It accounts for approximately 15% of newly diagnosed cases of leukemia in adults.

DIAGNOSIS

CML is characterized by a balanced genetic translocation, t(9;22) (q34;q11.2), involving a fusion of the Abelson murine leukemia (ABL1) gene from chromosome 9q34 with the breakpoint cluster region (BCR) gene on chromosome 22q11.2. This rearrangement is known as the Philadelphia chromosome. The molecular consequence of this translocation is the generation of a BCR::ABL1 fusion oncogene, which in turn translates into a BCR::ABL1 oncoprotein.

FRONTLINE THERAPY

Four tyrosine kinase inhibitors (TKIs), imatinib, dasatinib, bosutinib, and nilotinib, are approved by the United States Food and Drug Administration (FDA) for first-line treatment of newly diagnosed CML in the chronic phase (CML-CP). Clinical trials with second and third-generation TKIs in frontline CML-CP therapy reported significantly deeper and faster responses but had no impact on survival prolongation, likely because of their potent efficacy and the availability of effective TKIs salvage therapies for patients who have a cytogenetic relapse with frontline TKI therapy. All four TKIs are equivalent if the aim of therapy is to improve survival. In younger patients with high-risk disease and in whom the aim of therapy is to induce a treatment-free remission status, second-generation TKIs may be favored.

SALVAGE THERAPY

For CML post-failure on frontline therapy, second-line options include second and third-generation TKIs. Although potent and selective, these TKIs exhibit unique pharmacological profiles and response patterns relative to different patient and disease characteristics, such as patients' comorbidities and financial status, disease stage, and BCR::ABL1 mutational status. Patients who develop the T315I "gatekeeper" mutation display resistance to all currently available TKIs except ponatinib, asciminib, and olverembatinib. Allogeneic stem cell transplantation remains an important therapeutic option for patients with CML-CP and failure (due to resistance) of at least two TKIs and for all patients in advanced-phase disease. Older patients who have a cytogenetic relapse post-failure on all TKIs can maintain long-term survival if they continue a daily most effective/least toxic TKI, with or without the addition of non-TKI anti-CML agents (hydroxyurea, omacetaxine, azacitidine, decitabine, cytarabine, and others).

Cytogenetics and genomics in CML and other myeloproliferative neoplasms

Chronic myeloid leukemia is defined by the presence of the Philadelphia translocation t (9; 22) resulting in the BCR::ABL1 fusion. The other myeloproliferative neoplasms (MPN) subtypes also carry typical chromosomal abnormalities, which however are not pathognomonic for a specific entity of MPN. According to the WHO classification the distinction between these entities is still based on the integration of cytological, histopathological and molecular findings. Progression of CML into accelerated and blastic phase is usually driven by additional chromosome abnormalities and ABL1 kinase mutations. In the other MPN subtypes the additional mutations besides driver gene mutations in JAK2, MPL and CALR have a decisive impact on the propensity for progression. In addition, the sequence in which the driver mutations and risk conveying additional mutations have been acquired appears to play an important role. Here, we review cytogenetic and molecular changes in CML and MPN that should be evaluated during diagnosis and disease monitoring.

De novo accelerated phase of chronic myeloid leukemia should be recognized even in the era of tyrosine kinase inhibitors

Overall survival of patients classified according to the European LeukemiaNet 2020 classification. Chronic phase (CP), accelerated phase (AP), blast crisis (BC), low risk (LR), intermediate risk (IR), high risk (HR).

The Contemporary Role of Hematopoietic Stem Cell Transplantation in the Management of Chronic Myeloid Leukemia: Is It the Same in All Settings?

Hematopoietic stem cell transplantation (HSCT) for chronic myeloid leukemia (CML) patients has transitioned from the standard of care to a treatment option limited to those with unsatisfactory tyrosine kinase inhibitor (TKI) responses and advanced disease stages. In recent years, the threshold for undergoing HSCT has increased. Most CML patients now have life expectancies comparable to the general population, and therefore, the goal of therapy is shifting toward achieving treatment-free remission (TFR). While TKI discontinuation trials in CML show potential for achieving TFR, relapse risk is high, affirming allogeneic HSCT as the sole curative treatment. HSCT should be incorporated into treatment algorithms from the time of diagnosis and, in some patients, evaluated as soon as possible. In this review, we will look at some of the recent advances in HSCT, as well as its indication in the era of aiming for TFR in the presence of TKIs in CML.