Tyrosine Kinase Inhibitors Discontinuation Research Articles

Wczesny nawrót molekularny po odstawieniu terapii nilotynibem

Pojawienie się imatynibu, a następnie kolejnych inhibitorów kinaz tyrozynowych (TKI), doprowadziło do zrównania długości życia chorych na przewlekłą białaczkę szpikową (CML) z czasem przeżycia oczekiwanym w zdrowej populacji. Obecnie celem terapeutycznym dla dużej grupy pacjentów jest uzyskanie remisji wolnej od leczenia. Wyniki licznych badań wskazują, że spośród pacjentów, którzy osiągnęli stabilną głęboką odpowiedź molekularną (DMR) i odstawili leczenie TKI, 40–50% może pozostać w remisji. Kluczowe jest to, że pacjenci, u których następuje nawrót molekularny, nie doświadczają progresji choroby do fazy zaawansowanej i prawie zawsze odzyskują DMR po ponownym wdrożeniu leczenia. Poniżej przedstawiono opis przypadku pacjenta z CML, u którego z powodu nietolerancji imatynibu wdrożono nilotynib, a po kilku latach terapii lek odstawiono. Cztery tygodnie po przerwaniu leczenia u pacjenta doszło do utraty większej odpowiedzi molekularnej. Niezwłocznie wznowiono terapię nilotynibem i już po 3 miesiącach chory odzyskał DMR.

Interferon-α may help prevent molecular relapse of chronic myeloid leukemia after the discontinuation of tyrosine kinase inhibitors.

Background:Currently, the goal of chronic myeloid leukemia (CML) treatment is normal survival and good quality of life without life-long treatment, namely, “treatment-free remission” (TFR). At present, approximately only 50% of patients with CML with a deep molecular response are able to discontinue tyrosine kinase inhibitor (TKI) without experiencing molecular relapse [MR; loss of major molecular response (MMR)]. In addition, prior interferon (IFN) treatment is associated with a higher rate of TFR.Methods:We aimed to evaluate the feasibility of TKI discontinuation in Chinese patients with CML and determine whether IFN could prevent MR when used after TKI discontinuation in patients with 0.0032% <BCR-ABLIS ⩽0.1%. Therefore, we retrospectively analyzed the data of patients with CML who discontinued TKI treatment at our center.Results:Forty-nine patients who discontinued TKI therapy after achieving MR 4.5 were included in this study, and the median follow-up time from TKI discontinuation was 27 (7, 75) months. Nineteen patients eventually lost MMR, and the TFR rate of the 49 patients was 67% (95% confidence interval 53.6%, 80.3%) at 12 months. The duration of MR 4.5 ⩾54 months and duration of imatinib ⩾85 months were significantly associated with a higher TFR rate. Of the 22 patients with 0.0032% <BCR-ABLIS ⩽0.1%, 12 received IFN-α treatment. The median IFN-α therapy duration was nine (2, 18) months, and three patients eventually lost MMR. Three patients discontinued IFN-α after 2, 2.5, and 10 months, and maintained MMR for 9, 8, and 11 months after IFN discontinuation, respectively. Of the 10 patients not receiving IFN-α treatment, eight eventually lost MMR. The MR-free survival rate was significantly different between the patients treated with and those treated without IFN-α over 24 months (70.7% versus 15.0%, p = 0.002).Conclusion:These results indicate that after TKI discontinuation, IFN-α can be administered to patients with 0.0032% <BCR-ABLIS ⩽0.1%, which may help prevent MR.

Factors for Sustaining Molecular Remission after Discontinuation of Tyrosine Kinase Inhibitors Therapy in Chronic Myeloid Leukemia: Results of Non-Randomized Prospective Clinical Trial

Aim. To study the impact of different clinical and biological factors on sustaining molecular remission after discontinuation of tyrosine kinase inhibitors (TKI) therapy in chronic myeloid leukemia (CML) patients with a stable deep molecular response (MR). Materials &amp; Methods. The prospective multi-center trial on molecular remission sustainability after TKIs withdrawal, held from 2015 to 2019, enrolled 98 CML patients. The trial included patients with chronic phase CML treated with TKIs at least during 3 years and having a stable deep MR (&lt; МО4; BCR-ABL &lt; 0.01 %) during at least 2 years. Molecular monitoring was carried out every month during first 6 months after TKIs withdrawal, every 2 months during 0.5-1 year, and every 3 months after 1-year follow-up. In case of the loss of major MR (BCR-ABL &gt; 0.1 %) therapy was reinitiated. Results. Three-year molecular relapse-free survival was 51 % (95% confidence interval 41-61 %) in all patients, 25 % in patients with the failure of prior treatment discontinuation, and 53 % in patients who discontinued TKI therapy for the first time. According to univariate analysis, the following factors proved to be significant: persistance of deep MR, duration of therapy, and depth of MR. It was shown that TKI therapy duration, but not deep MR persistance, has independent prognostic value for the Russian population of CML patients. No significant differences were identified in 3-year molecular relapse-free survival in the groups of patients treated only with imatinib (55 %) compared with patients who received 2nd generation TKI (TKI2) as first-line (70 %; p = 0.26) and second-line (39 %; p = 0.09) therapy. However, duration of therapy in patients treated with TKI2 as first-line therapy was more than twice as short as in patients treated with imatinib as first-line therapy (median 41.5 vs. 96.4 months, respectively; p &lt; 0.0001). Conclusion. Longer therapy duration and MR depth (&lt; M04.5) before TKI withdrawal raise the probability of sustaining off-treatment remission. The study showed that molecular relapse-free survival does not significantly increase with the use of TKI2 as first-line treatment compared to imatinib. Nevertheless, TKI2 as first-line treatment enables to halve the duration of therapy needed to achieve comparable molecular relapse-free survival, as compared with imatinib.

Biological Mechanisms of Sustaining Deep Molecular Response in Chronic Myeloid Leukemia Upon Withdrawal of Tyrosine Kinase Inhibitors

The feasibility of treatment-free follow-up in chronic myeloid leukemia (CML) patients is an important issue in the era of tyrosine kinase inhibitors (TKI). The clinical trials of TKI withdrawal in case of a stable deep molecular response prove the probability of sustaining molecular remission in 40-60 % of patients. Treatment-free remission (TFR), even under persistence of residual leukemia cells, suggests that there are special biologically determined mechanisms of tumor cell proliferation control, which are independent of BCR-ABL kinase activity. The search for factors determining differences in residual leukemia clone kinetics upon TKI withdrawal is an objective which is crucial for understanding TFR as a new biological phenomenon. The review provides worldwide evidence dealing with the study of immunological, genetic, and other biological mechanisms underlying the control of minimal residual disease upon TKI discontinuation in CML patients.

Predictive indicators of successful tyrosine kinase inhibitor discontinuation in patients with chronic myeloid leukemia.

Clinical trials have demonstrated that some patients with chronic myeloid leukemia (CML) treated for several years with tyrosine kinase inhibitors (TKIs) who have maintained a molecular response can successfully discontinue treatment without relapsing. Treatment free remission (TFR) can be reached by approximately 50% of patients who discontinue. Despite having similar levels of deep molecular response and an identical duration of treatment, the factors that influence the successful discontinuation of CML patients remain to be determined. In this review we will explore the factors identified to date that can help predict whether a patient will successfully achieve TFR. We will also discuss the need for the identification of predictive biomarkers associated with a high probability of achieving TFR for the future personalized identification of patients who are suitable for the discontinuation of TKI treatment.

Out-of-Pocket Costs for Tyrosine Kinase Inhibitors and Patient Outcomes in EGFR- and ALK-Positive Advanced Non-Small-Cell Lung Cancer.

We investigated the association of out-of-pocket (OOP) costs for tyrosine kinase inhibitors (TKIs) with overall survival (OS) in epidermal growth factor receptor (EGFR)- and anaplastic lymphoma kinase (ALK)-positive advanced non-small-cell lung cancer (NSCLC). We secondarily investigated associations of TKI OOP costs with TKI adherence, duration of therapy (DOT), and TKI discontinuation. We used the Hutchinson Institute for Cancer Outcomes Research registry-claims database to identify patients with stage IV EGFR- or ALK-positive NSCLC; ≥ 1 claims for EGFR or ALK TKIs; and ≥ 3-month survival from TKI initiation. We estimated the average monthly TKI OOP costs per patient up to 3 months from TKI initiation, categorizing patients into quartiles of TKI OOP costs (Q1 < Q2 < Q3 < Q4). We conducted landmark analysis at 3 months from TKI initiation to compare Q1-3 v Q4 TKI OOP costs with respect to OS, TKI DOT, TKI adherence, and TKI discontinuation. Seventy-eight and twenty-seven patients comprised the Q1-3 and Q4 groups, respectively. Median monthly TKI OOP costs were $1,431 (Q1-3) v $2,888 (Q4). Compared with Q1-3, Q4 patients had inferior OS (adjusted hazard ratio [HR], 1.85; [95% CI, 1.11 to 3.10], similar TKI DOT (adjusted HR, 1.06; 95% CI, 0.53 to 2.15), decreased TKI adherence (adjusted odds ratio [OR], 0.28; 95% CI, 0.10 to 0.76), and higher TKI discontinuation rate (adjusted OR, 8.75; 95% CI, 2.59 to 29.52). Among patients with advanced EGFR- and ALK-positive NSCLC, higher TKI OOP costs are associated with decreased TKI adherence, a higher likelihood of TKI discontinuation, and inferior survival.

Discontinuation of Maintenance Tyrosine Kinase Inhibitors in Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia outside of Transplant

Background: The addition of tyrosine kinase inhibitors (TKIs) to chemotherapy has dramatically improved outcomes of patients with Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL). When allogeneic hematopoietic stem cell transplant (HSCT) is performed, maintenance TKI is generally given for a fixed duration. However, the optimal duration of TKI outside of HSCT remains unknown, and the common practice is to continue indefinitely. Here, we report characteristics and outcomes of 9 patients treated with chemotherapy + TKI without HSCT and later discontinued TKI. Methods: Among 188 patients with Ph-positive ALL who did not undergo HSCT, 9 of them discontinued maintenance TKI mainly due to side effects. Patients were closely monitored with serial PCR testing for the BCR-ABL1 transcript. Major molecular response (MMR) was defined as BCR-ABL1 transcript ≤0.1% on the international scale for p210 transcripts and a 3-log reduction from baseline for p190 transcripts. Deep molecular remission (DMR) was defined as the absence of quantifiable BCR-ABL1 transcripts with a sensitivity of 0.01%. Molecular relapse was defined as loss of MMR. Treatment-free remission (TFR) was defined from time of TKI discontinuation to molecular relapse, last follow-up, or death from any cause. Results: At the time of TKI discontinuation, transcript level was undetected in 6 patients, <0.01% in 2 patients, and 0.01% in another patient. Prior to discontinuation, the median duration of TKI therapy and of DMR was 70 and 47 months, respectively. No morphological relapse occurred. Three patients (33%) had molecular relapse at a median of 6 months. All 3 resumed TKI therapy, and 2 of them regained DMR after a median of 13 months. After a median follow-up of 49 months, the median TFR was not reached, and the 4-year TFR rate was 65%. The median duration of DMR in patients with and without molecular relapse was 22 and 58 months, respectively (p = 0.096). Conclusion: TKI discontinuation outside of HSCT in Ph-positive ALL in the setting of compelling toxicity may be safe only among a highly selected group of patients with deep and prolonged DMR undergoing close and frequent monitoring. Validation of these findings in prospective clinical trials is highly needed.

Digital PCR for BCR‐ABL1 Quantification in CML: Current Applications in Clinical Practice

Molecular monitoring of the BCR-ABL1 transcript for patients with chronic phase chronic myeloid leukemia (CML) has become increasingly demanding. Real-time quantitative PCR (qPCR) is the routinely used method, but has limitations in quantification accuracy due to its inherent technical variation. Treatment recommendations rely on specific BCR-ABL1 values set at timed response milestones, making precise measurement of BCR-ABL1 a requisite. Furthermore, the sensitivity of qPCR may be insufficient to reliably quantify low levels of residual BCR-ABL1 in patients in deep molecular response (DMR) who could qualify for an attempt to discontinue Tyrosine Kinase Inhibitor (TKI) therapy. We reviewed the current use of digital PCR (dPCR) as a promising alternative for response monitoring in CML. dPCR offers an absolute BCR-ABL1 quantification at various disease levels with remarkable precision and a clinical sensitivity reaching down to at least MR5.0. Moreover, dPCR has been validated in multiple studies as prognostic marker for successful TKI treatment discontinuation, while this could not be achieved using classical qPCR. dPCR may thus prospectively be the preferred method to reliably identify patients achieving treatment milestones after initiation of TKI therapy as well as for the selection and timing for TKI discontinuation.

A Retrospective Analysis about Frequency of Monitoring in Italian Chronic Myeloid Leukemia Patients after Discontinuation.

Successful discontinuation of tyrosine kinase inhibitors has been achieved in patients with chronic-phase chronic myeloid leukemia (CML). Careful molecular monitoring after discontinuation warrants safe and prompt resumption of therapy. We retrospectively evaluated how molecular monitoring has been conducted in Italy in a cohort of patients who discontinued tyrosine kinase inhibitor (TKI) treatment per clinical practice. The outcome of these patients has recently been reported—281 chronic-phase CML patients were included in this subanalysis. Median follow-up since discontinuation was 2 years. Overall, 2203 analyses were performed, 17.9% in the first three months and 38.4% in the first six months. Eighty-six patients lost major molecular response (MMR) in a mean time of 5.7 months—65 pts (75.6%) during the first six months. We evaluated the number of patients who would experience a delay in diagnosis of MMR loss if a three-month monitoring schedule was adopted. In the first 6 months, 19 pts (29.2%) would have a one-month delay, 26 (40%) a 2-month delay. Very few patients would experience a delay in the following months. A less intense frequency of monitoring, particularly after the first 6 months off treatment, would not have affected the success of treatment-free remission (TFR) nor put patients at risk of progression.

Assessment of Outcomes After Stopping Tyrosine Kinase Inhibitors Among Patients With Chronic Myeloid Leukemia

Tyrosine kinase inhibitors (TKIs) have been associated with improved survival of patients with chronic myeloid leukemia (CML) but are also associated with adverse effects, especially fatigue and diarrhea. Discontinuation of TKIs is safe and is associated with the successful achievement of treatment-free remission (TFR) for some patients. To evaluate molecular recurrence (MRec) and patient-reported outcomes (PROs) after TKI discontinuation for US patients with CML. The Life After Stopping TKIs (LAST) study was a prospective single-group nonrandomized clinical trial that enrolled 172 patients from 14 US academic medical centers from December 18, 2014, to December 12, 2016, with a minimum follow-up of 3 years. Participants were adults with chronic-phase CML whose disease was well controlled with imatinib, dasatinib, nilotinib, or bosutinib. Statistical analysis was performed from August 13, 2019, to March 23, 2020. Discontinuation of TKIs. Molecular recurrence, defined as loss of major molecular response (BCR-ABL1 International Scale ratio >0.1%) by central laboratory testing, and PROs (Patient-Reported Outcomes Measurement Information System computerized adaptive tests) were monitored. Droplet digital polymerase chain reaction (ddPCR) was performed on samples with undetectable BCR-ABL1 by standard real-time quantitative polymerase chain reaction (RQ-PCR). Of 172 patients, 89 were women (51.7%), and the median age was 60 years (range, 21-86 years). Of 171 patients evaluable for molecular analysis, 112 (65.5%) stayed in major molecular response, and 104 (60.8%) achieved TFR. Undetectable BCR-ABL1 by either ddPCR or RQ-PCR at the time of TKI discontinuation (hazard ratio, 3.60; 95% CI, 1.99-6.50; P < .001) and at 3 months (hazard ratio, 5.86; 95% CI, 3.07-11.1; P < .001) was independently associated with MRec. Molecular recurrence for patients with detectable BCR-ABL1 by RQ-PCR was 50.0% (14 of 28), undetectable BCR-ABL1 by RQ-PCR but detectable by ddPCR was 64.3% (36 of 56), and undetectable BCR-ABL1 by both ddPCR and RQ-PCR was 10.3% (9 of 87) (P ≤ .001). Of the 112 patients in TFR at 12 months, 90 (80.4%) had a clinically meaningful improvement in fatigue, 39 (34.8%) had a clinically meaningful improvement in depression, 98 (87.5%) had a clinically meaningful improvement in diarrhea, 24 (21.4%) had a clinically meaningful improvement in sleep disturbance, and 5 (4.5%) had a clinically meaningful improvement in pain interference. Restarting a TKI resulted in worsening of PROs. In this study, TKI discontinuation was safe, and 60.8% of patients remained in TFR. Discontinuation of TKIs was associated with improvements in PROs. These findings should assist patients and physicians in their decision-making regarding discontinuation of TKIs. Detectable BCR-ABL1 by RQ-PCR or ddPCR at the time of TKI discontinuation was associated with higher risk of MRec; clinical application of this finding should be confirmed in other studies. ClinicalTrials.gov Identifier: NCT02269267.

Tyrosine kinase inhibitor treatment discontinuation in chronic myeloid leukemia: patient views

Patients with chronic myeloid leukemia (CML) in deep molecular remission may discontinue tyrosine kinase inhibitor (TKI) treatment without relapse. The present study aims to gain insight into the views of CML patients on TKI treatment discontinuation and identify factors that are associated with their willingness to discontinue treatment. A cross-sectional study, among adult Dutch CML patients was conducted to assess willingness and their views on benefits of and concerns about discontinuation. A total of 185 patients participated of whom 76% were willing to discontinue TKI-treatment. Patients considered the absence of side effects the most important benefit whereas fear of disease recurrence was their most prominent concern. Adequate monitoring was the most important prerequisite for TKI-treatment discontinuation. However, ambiguity with respect to perquisites indicate that patients on long-term TKI treatment should be adequately informed both on the possibility to discontinue treatment and on its benefits, risks, and measures that address risks.

BCR-ABL1 Transcript Doubling Time after Imatinib Discontinuation for Treatment-Free Remission in Chronic Myeloid Leukemia in Chronic Phase: Predictor for Treatment-Free Remission Failure

BCR-ABL1 Transcript Doubling Time after Imatinib Discontinuation for Treatment-Free Remission in Chronic Myeloid Leukemia in Chronic Phase: Predictor for Treatment-Free Remission Failure

Single-Cell Roadmap of Immune Cell Response in Chronic Myeloid Leukemia

Only half of chronic myeloid leukemia (CML) patients in deep molecular remission are able to maintain treatment free remission (TFR) after tyrosine kinase inhibitor (TKI) discontinuation. Identifying predictive markers for TFR remains a key issue. The immunological control or eradication of TKI insensitive leukemic stem cells may contribute to successful cessation, as recent work has demonstrated that differences in immune cell compositions can be associated with better probability of TFR. In order to understand the precise immunological changes in CML, we profiled over 170,000 cells from 25 CML samples from different clinical phases (untreated, during TKI therapy and after TKI cessation) using single-cell RNA and T cell receptor (TCR) αβ sequencing (scRNA+TCRab-seq). We profiled both CD45+ sorted peripheral blood samples (n=20) and CD34+ sorted bone marrow samples (n=5). To understand antigen-specific responses, we profiled TCRs specific to tumor-antigen PR1 (n=12) and compared these to unsorted TCRβ-sequenced samples from CML (n=137) and healthy donors (n=786). To understand the distinctive immunological features in CML, we compared the immune system in CML (n=20) to those in other hematological and solid malignancies profiled with scRNA+TCRab-seq (n=9). We discovered NK cells to be the most unique feature in CML, as NK CD56dim cells were more abundant in CML patients (Padj&amp;lt;0.001) and the NK cell repertoire was more transcriptionally heterogenous and included otherwise rarely seen exhausted NK population with upregulated HAVCR2 and TIGIT expression (Padj &amp;lt;0.0001). Further, the NK cell maturation changed during TKI-treatment from an effector CD56dim state towards an adaptive NK-cell state. We sought to understand whether the immunological activity differs before and after TKI discontinuation in different clinical outcomes following discontinuation. Therefore, we reclustered the discontinuation samples from three different outcomes: TFR, early relapse (&amp;lt;6 months after cessation) or late relapse (&amp;gt;6 months). In all clinical outcomes, TKI cessation invigorated NK cell exhaustion and the most upregulated pathways included IFNg and TNFa via NFkB pathways. Patients with successful TFR had less differences in their immune system after cessation in comparison to relapsing patients, which could hint that their immune subsets were better prepared for the cessation. Unlike the early relapse patients' quiescent immune cells, the late relapse patients' immune subsets were active, but under pronounced inhibitory Treg signals, providing a clinically interesting approach to alter the outcome of these patients. Next, to understand how malignant CML cells evade or interact with the immune system, we analyzed CD34+ cells and calculated a BCR-ABL1 activity score. The most primitive CD34+ cells had lower BCR-ABL1 score and not as many immunological ligand-receptor pairs as their less primitive, highly BCR-ABL1 pathway expressing, counterparts (P&amp;lt;0.0001). LGALS9, that is expressed on both BCR-ABL1 high and low CD34+ cells, arose as one of the most interesting ligands mediating tumor-immune cell interactions and it has many potential receptors expressed by NK cells, including HAVCR2. Finally, we found that tumor-antigen PR1 is preferentially expressed on CD34+ cells with high BCR-ABL1 score. Most TCRs recognizing PR1 are restricted to individuals, but they share short amino-acid motifs that are shared across patients. Thus, we were able to generate an in silico tool to recognize PR1-specific TCRs from unsorted TCR-seq samples with high accuracy (AUC 0.91 from 10-fold cross validation). With our tool, we were able to show that anti-PR1 responses were more frequent in CML than in healthy donors (P&amp;lt;0.0001), are more expanded in bone-marrow than in blood (P&amp;lt;0.0001) and diversified during TKI treatment (P&amp;lt;0.0001). In the scRNA+TCRab-seq data, the anti-PR1 response differed between TFR and early relapse patient significantly at phenotype level, where the TFR patient had cytotoxic anti-leukemic response before TKI cessation, in comparison to the early relapse patient's exhausted and less cytotoxic PR1-specific cells. In conclusion, our results provide high-resolution insights into anti-leukemic immune responses in CML and how we could harness and monitor them to enable successful TKI cessations. Figure Disclosures Olsson-Strömberg: Pfizer: Research Funding. Hjorth-Hansen:Pfizer: Honoraria, Research Funding; Austrian Orphan Pharma: Honoraria, Research Funding; Bristol-Myers Squibb: Research Funding. Mustjoki:Pfizer: Research Funding; Novartis: Research Funding; BMS: Honoraria, Research Funding.

Optimal Duration of Imatinib Treatment / Deep Molecular Response for Treatment-Free Remission after Imatinib Discontinuation from a Canadian Tyrosine Kinase Inhibitor Discontinuation Trial

Optimal Duration of Imatinib Treatment / Deep Molecular Response for Treatment-Free Remission after Imatinib Discontinuation from a Canadian Tyrosine Kinase Inhibitor Discontinuation Trial

Retro-Prospective Observational Study on the Risk of Progression in Chronic Phase-Chronic Myeloid Leukemia (CML) Patients Eligible for Tyrosine Kinase Inhibitor Discontinuation (TFR-PRO)

Retro-Prospective Observational Study on the Risk of Progression in Chronic Phase-Chronic Myeloid Leukemia (CML) Patients Eligible for Tyrosine Kinase Inhibitor Discontinuation (TFR-PRO)

Blast MRD CML 1 Trial: Blockade of PD-1 Added to Standard Therapy to Target Measurable Residual Disease (MRD) in Chronic Myeloid Leukemia (CML)- a Phase II Study of Adding the Anti-PD-1 Pembrolizumab to Tyrosine Kinase Inhibitors in Patients with Chronic Myeloid Leukemia and Persistently Detectable Minimal Residual Disease: A Trial of the ECOG-ACRIN Cancer Research Group (EA9171)

Blast MRD CML 1 Trial: Blockade of PD-1 Added to Standard Therapy to Target Measurable Residual Disease (MRD) in Chronic Myeloid Leukemia (CML)- a Phase II Study of Adding the Anti-PD-1 Pembrolizumab to Tyrosine Kinase Inhibitors in Patients with Chronic Myeloid Leukemia and Persistently Detectable Minimal Residual Disease: A Trial of the ECOG-ACRIN Cancer Research Group (EA9171)

Discontinuation of Imatinib in Children with Chronic Myeloid Leukemia: An International Registry of Childhood Chronic Myeloid Leukemia (I-CML-Ped) Study

Background: Imatinib, a tyrosine kinase inhibitor (TKI) is currently proposed as first line therapy in children with chronic myeloid leukemia (CML) in chronic phase (CP). Studies in adults with CML demonstrated that 40 to 50% of patients with prolonged deep molecular response under TKI could discontinue TKI permanently without molecular relapse. However, data regarding TKI discontinuation in children with CML are limited. Methods: Using the ELN criteria we identified in the International Registry of Childhood Chronic Myeloid Leukemia 18 patients less than 18 years of age at diagnosis with CML in CP exhibiting under imatinib treatment sustained deep molecular response &amp;gt;MR4.0 (DMR) for ≥ 2 years and then discontinued the TKI. We retrospectively analyzed outcome of these patients and treatment-free remission rate (TFR) at various time points. Treatment with imatinib was resumed in case of molecular relapse defined as loss of major molecular response (MMR). Results: There were 11 boys and 7 girls. From diagnosis in CP until TKI discontinuation the 18 children showed no progression, resistance, warning or suboptimal response or switch to another TKI before discontinuation. Median age at diagnosis of CML was 11.9 years (range, 2.3 to 15.8 years) and median age at discontinuation of TKI was 16 years (range, 9 to 24 years). Median overall follow-up from diagnosis of CML was 107 months (range, 67-209 months). DMR was achieved after a median time of 12 months (range, 3 - 50 months) on imatinib. Before discontinuation median treatment duration of imatinib was 73.25 months (range, 32 to 109 months) and median duration of MR4.0 was 46.2 months (range, 23.9 to 98.6 months). Seven patients experienced molecular relapse 4.1 months (range, 1.9-6.4 months) after stopping and restarted imatinib. Two patient resumed imatinib 3.6 and 3.4 months after discontinuation because of increased in transcript level (from 0.001% to 0.01 and 0.012, respectively) but without loss of MMR. The median molecular follow up after discontinuation was 116 months (range, 71 to 209 months) for the patients without molecular relapse. The proportion of patients maintaining molecular free remission was 61% (95% CI, 38%-83%), 56% (95% CI, 33%-79%) and 56% (95% CI, 33%-79%) at 6, 12, and 36 months, respectively (Figure 1). Six of the 7 children who experienced molecular relapse after discontinuation again achieved MR4.0 at median of 4.7 months (range, 2.5-18 months) after restart of imatinib; the remaining patient achieved MMR but not DMR and was switched to Dasatinib. No withdrawal syndrome was observed in this cohort of 18 patients. In univariate analysis, age, sex, Sokal and ELTS scores, imatinib treatment duration before discontinuation and duration of DMR until imatinib discontinuation had no influence on treatment free remission. Conclusion: These data indicate that imatinib could be safely discontinued in children younger than 18 years of age at diagnosis of CML with sustained MR4.0 for at least 2 years under imatinib. Larger studies of TKI discontinuation in children with CML are needed in order to identify factors predicting treatment free remission. Disclosures Dalle: Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Medac: Consultancy, Honoraria; Orchard: Consultancy, Honoraria; Bellicum: Consultancy, Honoraria; Jazz Pharmaceuticals: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi-Genzyme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Honoraria; AbbVie Pharmacyclics: Membership on an entity's Board of Directors or advisory committees.

High Level of Successful TKI Discontinuation in Chronic Myeloid Leukemia (CML) Patients: Preliminary Results of AST-Argentina Stop Trial

Introduction: Treatment-free remission (TFR) is an emerging treatment goal for chronic myeloid leukemia (CML) patients in deep molecular response (DMR). Current evidence shows that 40%-60% of patients relapse while in TFR; and nearly all regain response once tyrosine kinase inhibitors (TKIs) treatment are reinitiated. However a robust predictor of prolonged TFR has not been reported yet. Considering real-life setting, 2 key factors may affect TFR outcome if not properly done: Access to serial molecular monitoring at optimal timepoints and quality laboratory terms as accuracy, sensitivity and rapid results. This motivated the creation of the AST study in our region to guarantee adequate molecular monitoring for TFR in Argentina and characterize new prognostic biomarkers helpful to identify more accurately patients who will be able to sustain TFR. We aimed to assess the proportion of patients with sustained major molecular response (MMR) after TKIs discontinuation and define precise conditions for stopping treatment. Methods: This prospective, multicentre Argentina Stop Trial (AST) trial is recruiting chronic phase CML patients under TKI treatment for at least ≥ 4 years, in DMR (≥MR4.0) sustained for ≥ 2 years in standardized laboratory, confirmed typical BCR-ABL1 transcripts b3a2 and/or b2a2 and aged &amp;gt; 18 years. Molecular tests are centralized in 2 harmonized laboratories and performed monthly for the first 6 months, every 2 months until the first year, and every 3 months during the second year. If patients lost MMR, TKI was restarted immediately. Molecular relapse Free Survival was estimated by Kaplan-Meier method. Difference between survival variables was evaluated through log-rank test. Multivariate analysis was performed through Cox proportional hazards model. The cutoffs of the numerical variables were considered according to the log-rank test. Results: Between February 2019 and July 2020, we evaluated 50 CML patients of whom 46 were enrolled from 7 centers in Argentina and 4 were screening failures. Recruitment was interrupted due to COVID-19 pandemic. Patient median age was 57.5 years (range 24-85). Before discontinuation, TKI treatment was as follows: Imatinib 37/46 (80%), Nilotinib 5/46 (11%) and Dasatinib 4/46 (9%), 2G-TKI as 1st line, 11% of the patients received non-branded treatment. Sokal risk score showed to be low in 22 patients (48%), intermediate in 14 (30%) and high in 10 (22%). Median follow-up was 10 months (range 4-17) and the estimated molecular relapse-free survival was 80.2% (95%CI 69-93) at 6 months Fig 1. Longer DMR durations before discontinuation were associated with increased probability of maintaining response at 6 and 12 months: 83.2% for patients who had &amp;gt;54 months in DMR vs 70% with &amp;lt;54 months and 72% vs 23.3% respectively (p=0.0453) Fig 2. Cox multivariate analysis was performed including different variables as age at diagnosis, time in DMR, time in TKI previous to discontinuation and Sokal risk. The only significant variable associated to improved prognosis was time in DMR (HR 2.8 95%CI 1.002-8.07 p=0.0495). Our cohort had a long time on TKI treatment previous to discontinuation, median 10.5 years (4.16-17.5) probably considering it a favorable factor for the high TFR rates described at 6 months. Among the 46 patients included, 15 (33%) lost MMR, all restarted treatment with the same TKI used before discontinuation, 12/15 (80%) regained MMR with a median time of 3 months (range1-8) and 9/15(60%) obtained MR 4.0 with a median time of 3 months (range1-5). Conclusion: This is the first multicenter study of TKI discontinuation in CML patients in Argentina showing that TKI can be safely discontinued in those who achieve and maintain a DMR before discontinuation. We observed high rates of molecular relapse free survival, although longer follow-up is needed. We must continue with this approach for patients participating in TFR trials or TFR programs in order to decrease the risk of relapse and make this goal a fact in our region. This discontinuation study will allow in a near future significant saving of economic resources and might improve patients quality of life specially in those who are currently experiencing treatment adverse events. Disclosures Pavlovsky: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Speakers Bureau; Pfizer: Speakers Bureau; Pint Pharma: Speakers Bureau. Varela:Novartis: Consultancy, Speakers Bureau. Pavlovsky:Janssen: Membership on an entity's Board of Directors or advisory committees, Other: travel grants, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Other: Travel grants, Speakers Bureau; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Varifarma: Speakers Bureau. Moiraghi:BMS: Speakers Bureau; Novartis: Speakers Bureau.

The Pivotal Role of Nicotinamide Phosphoribosyl Transferase in Chronic Myeloid Leukemia Cells Under Hypoxic Condition

Introduction: ABL tyrosine kinase inhibitors (TKIs) improved outcomes for patients with chronic myeloid leukemia (CML) and Philadelphia chromosome (Ph)-positive leukemia. However, ABL TKIs do not eliminate the leukemia stem cells (LSCs) in the bone marrow, which may represent the most important event in leukemia relapse after TKI discontinuation. Bone marrow is also considered a tissue with limited oxygen supply. Therefore, new approach against leukemia stem cells, which is presented in bone marrow under hypoxia, may improve the outcome of CML patients. Nicotinamide phosphoribosyl transferase (NAMPT) is the rate limiting enzyme of the primary pathway for maintaining cellular NAD+ and that regulates intracellular adenosine triphosphate (ATP) levels in mammalian cells. It has been reported that NAMPT expression is upregulated in several human cancers. Materials and methods: In this study, we established ABL TKI resistantin vitrocell line models (K562 imatinib-R, K562 nilotinib-R, K562 ponatinib-R and Ba/F3 T315I) and used Ph-positive leukemia cell lines. We also investigated whether NAMPT inhibitor could suppress Ph-positive leukemia cells including T315I mutation and ABL TKI resistant under hypoxic condition. Results: In chemical library screen of compounds, NAMPT inhibitor, CHS828 is selected the candidate drug for ABL TKI resistant cells under hypoxic condition. Drug repositioning and repurposing can be an important part of any drug discovery. Therefore, we examined NAMPT efficacy by using Ph-positive leukemia cell lines. We first investigated the NAMPT expression by microarray gene expression data from the online Gene Expression Omnibus (GEO). Gene expression of NAMPT is increased in CML patients compared to normal samples from the public microarray datasets of GSE13159. Protein expression of NAMPT is found in Ph-positive leukemia cell lines including ABL TKI resistant cells. In hypoxia, gene expression of NAMPT was increased in Ph-positive cells compare to normoxic condition. We next examined efficacy of NAMPT inhibitor, CHS828 in Ph-positive leukemia cell lines. We found that CHS828 treatment for 72 h decreased cell viability of Ph-positive cell lines in a dose dependent manner. We also found that CHS828 inhibited the proliferation of ABL TKI resistant cells (K562 imatinib-R, K562 nilotinib-R, K562 ponatinib-R) and T315I mutant Ba/F3 cells under hypoxic condition. The rate of cell cycle progression was delayed and cells were blocked in G2/M phase. Nuclear factor-kappaB (NF-kB) is also implicated in cancer development. CHS828 inhibited constitutive NF-kB activity in the time and dose dependent manner. Intracellular ATP, which is the most important source of energy for cellular reactions, was drastically decreased after CHS828 treatment. NAD+ plays a vital role in diverse cellular processes that govern human health and disease. Intracellular NAD+ was decreased after CHS828 treatment. The wound healing effect was evaluated at 0, 24, 48, and 72 h by using NIH3T3 cells. In wound healing results, CHS828 treatment inhibited cellular migration of NIH3T3 cells. We next investigated the efficacy of ABL TKI and CHS828 against Ph-positive leukemia cell lines. ABL TKI and CHS828 treatment induced cellular growth inhibition compared with each drug alone. Caspase 3/7 activity was also increased after ABL TKIs and CHS828 treatment. ABL TKI and CHS828 reduced the colony formation ability of Ph-positive cells under hypoxic condition. Thein vivoefficacies of one of ABL TKI, ponatinib and CHS828 were evaluated in a mouse xenograft model. Ponatinib and CHS828 inhibited the growth of T315I mutant Ba/F3 cellsin vivomore than the control vehicle. We also found that co-treatment with ponatinib and CHS828 increased mouse survival. Combination treatment with ponatinib and CHS828 was also well tolerated, with no animal deaths in the treated mice. Conclusion: The results of our study indicate that the ABL TKI and CHS828 may be a powerful strategy against Ph-positive cells including ABL TKI resistant cells and provide the promising clinical relevance as a candidate drug for treatment of CML stem cells of the bone marrow microenvironment under hypoxic condition. Disclosures No relevant conflicts of interest to declare.

Excellent Outcomes Achieved with Medical Management of Chronic Phase CML Patients with Non-Hematologic TKI Intolerance

Introduction:Tyrosine kinase inhibitor (TKI) intolerance is commonly encountered in patients with chronic myeloid leukemia in chronic phase (CML-CP). Clinical trials define non-hematologic TKI intolerance as grade 3-4 toxicities, but lower grade toxicities may also impair patients' quality of life and lead to changes in medical management. We sought to compare TKI-intolerant and -tolerant CML-CP patients and their clinical outcomes, including molecular responses, rates of progression, survival, and utilization of allogeneic stem cell transplant (alloSCT). Methods:We performed a single-center, retrospective cohort study of active CML-CP patients in our Hematology clinic between January 2017 and December 2019. We defined TKI intolerance as any grade non-hematologic toxicity that led to a change in TKI management, such as dose reduction or change of TKI. We also reviewed CML-CP patients who underwent alloSCT in the TKI era (2002-2019). AlloSCT patients were identified for chart review by ICD-10 codes and query of the institution's transplant database. Descriptive statistics, Chi-Square tests, and two-tailed t-tests were used to summarize the data. Results:We identified 216 CML-CP patients (Table 1), and 161 (74.5%) met criteria for non-hematologic TKI intolerance. The median age was 59 years-old in TKI-intolerant patients and 49 in tolerant patients (P=0.011). Most patients experienced TKI-intolerance from symptoms (93.2%, n=150); symptoms included fatigue (n=77, 59.2%), arthralgias (n=36, 27.7%), nausea (n=29, 22.3%), headache (n=16, 12.3%), and edema (n=15, 11.5%). The remaining patients were TKI-intolerant based on abnormal laboratory findings such as transaminitis or hyperglycemia (6.8%, n=11/161). Of the 161 TKI-intolerant patients at last follow-up, 130 (80.7%) remained on TKI, 19 (11.8%) were on prescribed discontinuation, 6 (3.72%) were non-adherent, 5 (3.1%) were off TKI for non-CML medical problems, and 1 (0.6%) was on omacetaxine. Dose reductions occurred in the majority who remained on TKIs (n=103/130, 79.2%) and prior to TKI discontinuation (n=13/19, 68.4%). Most TKI-intolerant patients (n=122/161, 75.8%) switched TKIs, with a median of 2 agents used (range 1-5). Of 55 TKI-tolerant patients, 46 (83.6%) were on TKI, 8 (14.5%) were on discontinuation, and 1 (1.8%) was non-adherent. Only 19.6% (n=9/46) patients were dose-reduced, and they rarely changed TKIs (median of 1 agent used). MR4.5 was achieved in 49% (n=79/161) of TKI-intolerant and 41.8% (n=23/55) of TKI-tolerant patients. Only 1 patient in each group progressed to accelerated phase. TKI-intolerant and -tolerant patients had similar times since diagnosis (with a median follow up of 81.7 months and 79.7 months, respectively). Five of 161 (3.1%) TKI-intolerant patients died, all from causes unrelated to CML and TKI therapy. None of the TKI-tolerant patients died during the abstraction period. Twenty CML-CP patients underwent alloSCT from year 2002-2019; 10 (50%) were transplanted for TKI intolerance without other transplant indications (Tables 2 and 3). Three of those 10 patients also had hematologic intolerance. Four (40%) TKI-intolerant patients resumed TKI post-transplant: 3 for disease relapse, 1 for sclerotic GVHD. Seven (70%) developed GVHD, with most cases being chronic (n=6), extensive (n=6), and severe/moderate (n=6). While 80% of patients achieved MR4.5 post-transplant (n=8/10), 30% (n=3/10) experienced transplant-related mortality (TRM) with a mean post-transplant survival of 38.5 months; the remaining 7 patients were alive at a median follow-up of 37.1 months. Conclusion: CML-CP patients with non-hematologic TKI-intolerance achieved similar clinical outcomes as TKI-tolerant patients despite dose reductions and/or switching TKIs. The use of alloSCT was rare in our practice, and CML-CP patients transplanted for TKI intolerance commonly resumed TKI post-alloSCT and frequently developed extensive GVHD. In light of the high survival rate achieved with medical management in CML-CP patients with non-hematologic TKI-intolerance, including no disease- or treatment-related deaths, this analysis does not support the use of alloSCT for patients with non-hematologic TKI-intolerance. Disclosures Schoenbeck: American Society of Hematology:Research Funding.Olin:Astellas:Other: Site PI;Genentech:Consultancy;Daiichi Sankyo:Other: Site PI;Amgen:Consultancy;Genentech:Other: Site PI;Pfizer:Other: Site PI.Logan:Amphivena:Research Funding;Autolus:Research Funding;Jazz:Research Funding;Kadmon:Research Funding;Kite:Research Funding;Pharmacyclics:Research Funding;Abbvie:Consultancy;Amgen:Consultancy;Novartis:Consultancy.Smith:Revolution Medicines:Other: Research Support, Research Funding;Abbvie:Other: Research Support, Research Funding;FujiFilm:Other: Research support, Research Funding;Daiichi Sanyko:Consultancy, Honoraria;Astellas Pharma:Honoraria, Other: Research Support, Research Funding;Sanofi:Honoraria.Shah:Bristol-Myers Squibb:Research Funding.