Efficacy and safety of nilotinib in chronic myeloid leukaemia patients who failed to achieve a treatment-free remission period after imatinib discontinuation: Results of the French Nilo post-STIM study

Cases of Patients Treated in Countries With Limited Resources and Discussed by Experts of the International CML Foundation (iCMLf)-Case No. 2: Treatment-Free Remission After 9 Years of Imatinib Treatment Without Prior Achievement of Sustained Deep Molecular Response

Pediatric chronic myeloid leukemia (pCML) is a rare malignancy that nowadays is treated upfront with tyrosine kinase inhibitors (TKIs). As demonstrated in adult CML patients, achieving deep molecular response (DMR) and maintaining this status over 2 years results in the opportunity to discontinue TKI therapy. Following cessation, this treatment-free remission (TFR) status is successfully achieved by approximately 50% of the patients, while the other half experience molecular relapse within ≤ 6 months, requiring a TKI restart. As pCML accounts for only 2%-3% of all childhood leukemias, experience and familiarity with this disease, especially with stopping attempts, are still very limited. Small pCML cohorts enrolled in stopping TKI trials, with strict criteria applied for both depth and maintenance of DMR, have demonstrated the achievable TFR success rates seem comparable to adults. However, recommendations for considering TFR in pCML have yet to be defined. We report on a 9-year-old Brazilian boy diagnosed with CML in a chronic phase. He was treated with imatinib and achieved a molecular response (BCR::ABL1 transcript rate < 0.1%) at Month 12. Not achieving DMR, he responded well, but not optimally, to TKI therapy. Contrary to existing guidelines on TKI cessation in adults, after 9 years, imatinib was stopped. With a follow-up of 24 months, the patient is in TFR and now maintains DMR successfully. With the support of the International CML Foundation (iCMLf), which aims to improve outcomes for CML patients globally, this rare case from Brazil is discussed from the perspective of a pediatric hemato-oncologist from a high-income country, a pediatric hemato-oncologist from a low- and middle-income country, an adult CML hematologist, and the treating physician. Sharing cases of pCML in LMICs and highlighting the resources offered by the iCMLf, particularly the Knowledge Center (available online), will hopefully improve the expertise on pCML treatment worldwide.

Treatment-free remission as a new goal in the management of chronic myeloid leukemia: Clinical and biological aspects

The therapeutic armamentarium of chronic myeloid leukemia (CML) has dramatically improved after small molecule tyrosine kinase inhibitors (TKIs) targeting BCR::ABL1 became available, with a life expectancy now close to that of the general population. Although highly effective, these drugs also have a toxicity profile that is often mild to moderate, but sometimes severe. Indeed, long-term treatment with TKIs can lead to chronic adverse events that can negatively affect patients' quality of life and can promote significant morbidity and mortality, particularly in the case of second- or third-generation TKIs. Treatment discontinuation has therefore become an emerging goal for CML patients and numerous studies have evaluated in off-TKI subjects what requirements are appropriate for an attempt at treatment-free remission (TFR). TFR eligibility is currently limited to a small population of subjects with both deep and sustained molecular responses to TKIs. For those attempting TFR, average success rates are promising, with 25%-30% of patients experiencing prolonged TFR. In case of failure to maintain sustained TFR, safety results to date are reassuring, with almost all patients responding successfully to resumption of TKIs, and advanced-phase disease progression representing a very rare event. The purpose of this review is to discuss guidelines for TKI discontinuation, clinical advances from clinical trials and real-life experiences, and describe areas of research, particularly regarding the biological factors capable of predicting the success of TFR.

Treatment free remission (TFR) after second-generation tyrosine kinase inhibitors (2G-TKIs) treatment in chronic myeloid leukemia (CML): from feasibility to safety

INTRODUCTION

Chronic myeloid leukemia (CML) prevalence is currently increasing due to the great efficacy of tyrosine kinase inhibitor (TKI) therapy. Discontinuation of treatment in the long-term, owing to avoid off-target side effects or treatment-free remission (TFR), has become an additional treatment goal in CML patients who achieved a deep molecular response (DMR). Second-generation TKIs (2 G-TKIs) have a significantly higher rate of DMR than imatinib. Hence, especially in young patients with a strategy of TFR, 2 G-TKIs are becoming the most frequently used TKIs and may increase TFR attempts in the future.

AREAS COVERED

In this review, the main findings extrapolated from clinical trials and real-life evidence regarding 2 G-TKIs discontinuation were discussed, through broad research on Medline, Embase, and archives from EHA and ASH congresses.

EXPERT OPINION

Overall, TFR rate after 2 G-TKIs is ranging from 40% to 60% for selected patients with sustained DMR and it can be considered a safe procedure, that have become, nowadays, a daily practice. However, many crucial aspects regarding treatment choices, timings, as well as predictive factors, patient communication, and optimal strategies need to be better clarified to improve successful TFR rate.

The Mozart effect in chronic myeloid leukaemia

Clinical research has not been able to establish whether the differences between first- and second-generation BCR-ABL 1 kinase inhibitors are clinically relevant with regard to outcome. In the study by Alcazer et al., a relevant difference seems to emerge-paradoxically in the absence of the drugs-as demonstrated by differences in the relapse kinetics after cessation of therapy. Commentary on: Alcazer et al. Kinetics of molecular recurrence after tyrosine kinase inhibitor cessation in chronic phase chronic myelogenous leukaemia patients. Br J Haematol 2024;204:1536-1539.

Second Treatment-Free Remission Attempt in Patients with Chronic Myeloid Leukemia

Long-term survival outcomes of patients with chronic myeloid leukemia in the chronic phase are now similar to those of the general population, following the introduction of ABL1 tyrosine kinase inhibitors (TKIs). Approximately 40% to 80% of patients with chronic myeloid leukemia successfully achieved treatment-free remission after the first attempt of TKI discontinuation (TFR1), after achieving a durable deep molecular response. However, the possibility of achieving treatment-free remission after a second attempt of TKI discontinuation (TFR2) remains unclear. Therefore, we reviewed current TFR2 studies to clarify the feasibility of achieving TFR2. We identified 5 TFR2 clinical trials and 2 real-world reports. TFR2 attempt may be feasible after retreatment with imatinib, nilotinib, or dasatinib. Patients who have achieved MR4.0 or deeper durable molecular remission are eligible to enter the TFR2 phase. Imatinib is well tolerated and can be administered for consolidative treatment before the TFR2 attempt, whereas drug-related adverse effects of nilotinib or dasatinib affect their tolerability and might lead to discontinuation. Late onset relapse (> 1 year or > 2 year) was often reported, thus careful monitoring is needed.

Treatment-free remission after a second TKI discontinuation attempt in patients with Chronic Myeloid Leukemia re-treated with dasatinib - interim results from the DAstop2 trial

Tyrosine kinase inhibitor (TKI) discontinuation in chronic myeloid leukemia (CML) has become part of routine care for patients with a sustained deep molecular response (DMR). Approximately 50% experience a molecular relapse upon TKI cessation. Most of them quickly regain DMR upon TKI resumption. Whether these patients can achieve a second treatment-free remission (TFR) remains unclear. DAstop2 (ClinicalTrials.gov ID: NCT03573596) is a prospective study including patients with a failed first TFR attempt re-treated with any TKI for ≥ one year. Upon entering the study, patients received the TKI dasatinib for additional two years. Patients with sustained DMR for ≥1 year qualified for a second TKI stop. Ninety-four patients were included between Oct 2017-Dec 2021. At the time of data analysis, 62 patients had attempted a 2nd stop. After a median follow-up of 27 months from 2nd stop, TFR rates were 61, 56 and 46% at 6, 12 and 24 months respectively. No progression to advanced stage disease was seen and 87% had re-achieved MR4 within a median of 3 months from TKI re-initiation. In summary, we show that a 2nd TFR attempt after dasatinib treatment is safe, feasible and TFR rates seem in the range of those reported in trials of a first TKI stop.

Clinical Insights into Structure, Regulation, and Targeting of ABL Kinases in Human Leukemia

Chronic myeloid leukemia is a multistep, multi-lineage myeloproliferative disease that originates from a translocation event between chromosome 9 and chromosome 22 within the hematopoietic stem cell compartment. The resultant fusion protein BCR::ABL1 is a constitutively active tyrosine kinase that can phosphorylate multiple downstream signaling molecules to promote cellular survival and inhibit apoptosis. Currently, tyrosine kinase inhibitors (TKIs), which impair ABL1 kinase activity by preventing ATP entry, are widely used as a successful therapeutic in CML treatment. However, disease relapses and the emergence of resistant clones have become a critical issue for CML therapeutics. Two main reasons behind the persisting obstacles to treatment are the acquired mutations in the ABL1 kinase domain and the presence of quiescent CML leukemia stem cells (LSCs) in the bone marrow, both of which can confer resistance to TKI therapy. In this article, we systemically review the structural and molecular properties of the critical domains of BCR::ABL1 and how understanding the essential role of BCR::ABL1 kinase activity has provided a solid foundation for the successful development of molecularly targeted therapy in CML. Comparison of responses and resistance to multiple BCR::ABL1 TKIs in clinical studies and current combination treatment strategies are also extensively discussed in this article.

Final report of TKI discontinuation trial with dasatinib for the second attempt of treatment-free remission after failing the first attempt with imatinib: Treatment-free Remission Accomplished by Dasatinib (TRAD) study

Multiple studies have reported a significant treatment-free remission (TFR) rate of 50%-60% in patients with chronic myeloid leukaemia (CML) who discontinue tyrosine kinase inhibitor (TKI) therapy. However, the remaining half of these patients still require re-initiation of TKI therapy for leukaemia control. It remains unclear if TKI drugs should be switched for re-therapy in patients who failed the first TFR (TFR1) attempt. Our study attempted to determine whether dasatinib therapy after TFR1 failure post-imatinib discontinuation could improve the likelihood of TFR2. Of 59 patients who lost molecular response after imatinib discontinuation for TFR1, 55 patients (93.2%) were treated with dasatinib, of whom 49 (89.1%) regained MR4.5 or deeper response, with a median time of 1.85 months to achieve MR4.5. Dasatinib was discontinued in 35 patients for TFR2 attempt, of whom 26 patients (74.28%) lost MMR and 6 (17.14%) MR4. Risk factor analysis for the TFR2 after dasatinib discontinuation suggested three significant factors: (1) doubling time of BCR::ABL1 transcript following TFR1 attempt, (2) rapid regaining of molecular response following dasatinib therapy and (3) undetectable BCR::ABL1 transcript prior to TFR2 attempt. The present study showed that dasatinib does not increase the TFR2 rate in general, but a selected group of patients could benefit from this approach.