Discontinuation of Tyrosine Kinase Inhibitors in Patients with Chronic Myeloid Leukemia: a Review of the Biological Factors Associated with Treatment-Free Remission

Tyrosine Kinase Inhibitor Discontinuation in Chronic Myeloid Leukemia: Strategies to Optimize Success and New Directions

PURPOSE OF REVIEW

The discovery that patients suffering from chronic myeloid leukemia who obtain deep and long-lasting molecular responses upon treatment with tyrosine kinase inhibitors may maintain their disease silent for many years after therapy discontinuation launched the era of treatment-free remission as a key management goal in clinical practice. The purpose of this review on treatment-free remission is to discuss clinical advances, highlight knowledge gaps, and describe areas of research.

RECENT FINDINGS

Patients in treatment-free remission are a minority, and it is believed that some may still retain a reservoir of leukemic stem cells; thus, whether they can be considered as truly cured is uncertain. Strengthening BCR::ABL1 inhibition increases deep molecular responses but is not sufficient to improve treatment-free remission, and we lack biomarkers to identify and specifically target residual cells with aggressive potential. Another level of complexity resides in the intra- and inter-patient clonal heterogeneity of minimal residual disease and characteristics of the bone marrow environment. Finding determinants of deep molecular responses achievement and elucidating varying biological mechanisms enabling either post-tyrosine kinase inhibitor chronic myeloid leukemia control or relapse may help develop innovative and safe therapies. In the light of the increasing prevalence of CML, targeting the residual leukemic stem cell pool is thought to be the key.

Exploration of treatment-free remission in CML, based on molecular monitoring

BACKGROUND

Typical chronic myelogenous leukemia (CML) is a myeloproliferative neoplasm caused by t(9; 22)(q34; q11) translocation. This chromosomal translocation forms the BCR::ABL1 fusion gene. The tyrosine kinase encoded by the BCR::ABL1 is considered to be the main pathogenic diver. BCR::ABL1 is not only a therapeutic target, but also a monitoring target. Monitoring of BCR::ABL1 reveals the progression of the disease and guides the next treatment. Now for CML, the target of treatment has been focused on treatment-free remission (TFR).

METHODS

We conducted a literature review of current developments of treatment-free remission and molecular monitoring methods.

RESULTS

More effective and sensitive CML monitoring methods such as digital droplet PCR (ddPCR) and next generation sequencing (NGS) have further studied the measurable residual disease (MRD) and clonal heterogeneity, which provides strong support for the exploration of TFR. We discussed some of the factors that may be related to TFR outcomes at the molecular level, along with some monitoring strategies.

CONCLUSION

Currently, predictive indicators for treatment-free remission outcomes and recurrence are lacking in clinical practice. In future, treatment-free remission research should focus on combining the clinical indicators with molecular monitoring and biological markers to personalize patient conditions and guide clinicians to develop individualized treatment plans, so that more patients with CML can achieve safer and stabler treatment-free remission.

Effect of BCR::ABL1 transcript type and droplet digital polymerase chain reaction on successful treatment-free remission in chronic myeloid leukemia patients who discontinued tyrosine kinase inhibitor

Background

Droplet digital polymerase chain reaction (ddPCR) is an exact method of measurement.

Objectives

We conducted this study to identify the prognostic factors for successful treatment-free remission in patients with chronic-phase chronic myeloid leukemia who discontinued tyrosine kinase inhibitors (TKIs). We also aimed to validate ddPCR for predicting molecular relapse.

Design

This is a prospective, multicenter study.

Methods

We enrolled patients treated with TKIs for at least 3 years with a confirmed sustained deep molecular response (DMR) for at least 1 year. TKI was re-administered in patients who experienced the loss of major molecular response (MMR).

Results

A total of 66 patients from five institutions in South Korea were enrolled. During a median follow-up period of 16.5 months, 29/66 (43.9%) patients experienced molecular relapse; the probability of molecular relapse-free survival (RFS) at 6 or 12 months after TKI discontinuation was 65.6% or 57.8%, respectively, with most molecular relapses occurring within the first 7 months. All patients who lost MMR were re-treated with TKI, and all re-achieved MMR at a median of 2.8 months. E14a2 transcript type (p = 0.005) and longer DMR duration (⩾48 months) prior to TKI discontinuation (p = 0.002) were associated with prolonged molecular RFS and with sustained DMR. Patients with both e13a2 transcript type and detectable BCR::ABL1 (⩾MR5.0) by ddPCR at the time of TKI discontinuation showed shorter duration of molecular RFS (p = 0.015).

Conclusion

Our data suggest that transcript type and BCR::ABL1 transcript levels on ddPCR should be taken into consideration when deciding whether to discontinue TKI therapy.

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.

Immunomodulatory Activity of the Tyrosine Kinase Inhibitor Dasatinib to Elicit NK Cytotoxicity against Cancer, HIV Infection and Aging

Tyrosine kinase inhibitors (TKIs) have been extensively used as a treatment for chronic myeloid leukemia (CML). Dasatinib is a broad-spectrum TKI with off-target effects that give it an immunomodulatory capacity resulting in increased innate immune responses against cancerous cells and viral infected cells. Several studies reported that dasatinib expanded memory-like natural killer (NK) cells and γδ T cells that have been related with increased control of CML after treatment withdrawal. In the HIV infection setting, these innate cells are associated with virus control and protection, suggesting that dasatinib could have a potential role in improving both the CML and HIV outcomes. Moreover, dasatinib could also directly induce apoptosis of senescence cells, being a new potential senolytic drug. Here, we review in depth the current knowledge of virological and immunogenetic factors associated with the development of powerful cytotoxic responses associated with this drug. Besides, we will discuss the potential therapeutic role against CML, HIV infection and aging.

Chronic Myeloid Leukemia, from Pathophysiology to Treatment-Free Remission: A Narrative Literature Review

Chronic myeloid leukemia (CML) is one of the most common leukemias occurring in the adult population. The course of CML is divided into three phases: the chronic phase, the acceleration phase, and the blast phase. Pathophysiology of CML revolves around Philadelphia chromosome that constitutively activate tyrosine kinase through BCR-ABL1 oncoprotein. In the era of tyrosine kinase inhibitors (TKIs), CML patients now have a similar life expectancy to people without CML, and it is now very rare for CML patients to progress to the blast phase. Only a small proportion of CML patients have resistance to TKI, caused by BCR-ABL1 point mutations. CML patients with TKI resistance should be treated with second or third generation TKI, depending on the BCR-ABL1 mutation. Recently, many studies have shown that it is possible for CML patients who achieve a long-term deep molecular response to stop TKIs treatment and maintain remission. This review aimed to provide an overview of CML, including its pathophysiology, clinical manifestations, the role of stem cells, CML treatments, and treatment-free remission.