Defining Higher-Risk Chronic Myeloid Leukemia: Risk Scores, Genomic Landscape, and Prognostication

Mechanisms underlying therapeutic resistance of tyrosine kinase inhibitors in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a malignant clonal disease involving hematopoietic stem cells that is characterized by myeloid cell proliferation in bone marrow and peripheral blood, and the presence of the Philadelphia (Ph) chromosome with BCR-ABL fusion gene. Treatment of CML has dramatically improved since the advent of tyrosine kinase inhibitors (TKI). However, there are a small subset of CML patients who develop resistance to TKI. Mutations in the ABL kinase domain (KD) are currently recognized as the leading cause of TKI resistance in CML. In this review, we discuss the concept of resistance and summarize recent advances exploring the mechanisms underlying CML resistance. Overcoming TKI resistance appears to be the most successful approach to reduce the burden of leukemia and enhance cures for CML. Advances in new strategies to combat drug resistance may rapidly change the management of TKI-resistant CML and expand the prospects for available therapies.

The Success of Treatment Free Remission in Chronic Myeloid Leukaemia in Clinical Practice: A Single-Centre Retrospective Experience from South Africa

Introduction

Chronic myeloid leukaemia (CML) management has evolved from a disease once considered to be incurable just over 2 decades ago to that of one of a "functional cure" as defined by the sustained molecular response on stopping tyrosine kinase inhibitor(TKI) therapy. The next goal of CML management has been treatment-free remission (TFR). The past 4 years have seen much international data on TFR attempts in CML in clinical practice. However, Africa as a continent has lagged behind the rest of the world, in keeping up with the latest trends in CML management, and so this study aims to address this gap by assessing the outcome of TFR in CML in a single centre in South Africa (SA).

Methods

We conducted a retrospective cohort study in 12 CML patients in the chronic phase to assess the success of TKI discontinuation. The patients were treated in King Edward VIII Hospital (KEH), a tertiary, academic hospital in KwaZulu-Natal, South Africa, and the study period was from June 2020 to May 2022. Patients included had to have been on TKI therapy for a minimum of 5 years and achieved a deep molecular response (DMR) for a minimum period of 3 years.

Results

The overall TFR cohort showed a success rate of 75% at a median follow-up of 12 months. All patients who failed TFR, defined as a loss of major molecular remission (MMR), failed within 6 months of stopping TKI therapy. All patients who failed TFR regained DMR after retreatment with TKI, with no disease progression reported. The only factor influencing the success of TFR was the total period of TKI therapy.

Conclusion

Despite our study having a small cohort of patients, this study demonstrated that TFR in CML is an attainable goal, even in a resource-limited setting.

Management of chronic myeloid leukemia in 2023 - common ground and common sense

With the improving knowledge of CML and its management, the goals of therapy need to be revisited to ensure an optimal use of the BCR::ABL1 TKIs in the frontline and later-line therapy of CML. In the frontline therapy of CML in the chronic phase (CML-CP), imatinib and the three second-generation TKIs (bosutinib, dasatinib and nilotinib) are associated with comparable survival results. The second-generation TKIs may produce earlier deep molecular responses, hence reducing the time to reaching a treatment-free remission (TFR). The choice of the second-generation TKI versus imatinib in frontline therapy is based on the treatment aims (survival, TFR), the CML risk, the drug cost, and the toxicity profile with respect to the patient's comorbidities. The TKI dosing is more flexible than has been described in the registration trials, and dose adjustments can be considered both in the frontline and later-line settings (e.g., dasatinib 50 mg frontline therapy; dose adjusted schedules of bosutinib and ponatinib), as well as during an ongoing TKI therapy to manage toxicities, before considering changing the TKI. In patients who are not candidates for TFR, BCR::ABL1 (International Scale) transcripts levels <1% are acceptable, result in virtually similar survival as with deeper molecular remissions, and need not warrant a change of TKI. For patients with true resistance to second-generation TKIs or with the T315I gatekeeper mutation, the third-generation TKIs are preferred. Ponatinib should be considered first because of the cumulative experience and results in the CML subsets, including in T315I-mutated CML. A response-based dosing of ponatinib is safe and leads to high TKI compliance. Asciminib is a third-generation TKI with possibly a better toxicity profile, but lesser activity in T315I-mutated CML. Olverembatinib is another potent third-generation TKI with early promising results.