scholarly journals Discontinuation of dasatinib or nilotinib in chronic myeloid leukemia: interim analysis of the STOP 2G-TKI study

Blood ◽  
2017 ◽  
Vol 129 (7) ◽  
pp. 846-854 ◽  
Author(s):  
Delphine Rea ◽  
Franck E. Nicolini ◽  
Michel Tulliez ◽  
François Guilhot ◽  
Joelle Guilhot ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Interim Analysis ◽  
Myeloid Leukemia ◽  
First Line ◽  
Molecular Responses ◽  
Key Points ◽  
Treatment Free Remission

Key Points First-line or subsequent dasatinib or nilotinib can be safely stopped in CML patients with deep and long-lasting molecular responses. A suboptimal response or resistance prior to dasatinib or nilotinib is associated with significantly worse treatment-free remission.

scholarly journals First Interim Analysis of the Italian Dante Study: De-Escalation before Treatment-Free Remission in Patients with Chronic Myeloid Leukemia Treated with First-Line Nilotinib

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 1474-1474
Author(s):  
Massimo Breccia ◽  
Elisabetta Abruzzese ◽  
Fabio Stagno ◽  
Alessandra Iurlo ◽  
Fabrozio Pene ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Median Time ◽  
Interim Analysis ◽  
Myeloid Leukemia ◽  
Molecular Response ◽  
First Line ◽  
Full Dose ◽  
Consolidation Phase ◽  
Treatment Free Remission

Abstract Introduction: Treatment-free remission (TFR) in chronic myeloid leukemia (CML) is demonstrated to be achievable and recommended for patients (pts) in sustained deep molecular response (sDMR) who can discontinue tyrosine kinase inhibitor (TKI) treatment and maintain responses in ~50% of cases. While the feasibility and safety of TKI cessation have been largely demonstrated, the strategies of TFR optimization are yet to be clarified. Studies (eg. DESTINY) investigating de-escalation, mainly after imatinib, suggested that a stepwise approach may favor TFR outcome. We present the interim results of the phase 2, prospective, multicenter DANTE study (NCT03874858) evaluating de-escalation and TFR in Italian pts with CML in chronic phase (CML-CP) treated with nilotinib (NIL). Methods: Adults with CML-CP treated with NIL 300 mg twice daily (bid) in first-line for ≥3 years who achieved sDMR for ≥1 year (≥MR 4.0; BCR-ABL level ≤0.01% IS) were enrolled in 27 centers. The study consisted of 4 phases: screening (week [wk] −4-0), consolidation (wk 0-48), TFR (wk 48-144), and follow-up (until wk 144). Ongoing treatment with ≥400 mg/day dose was allowed at study entry. During consolidation, pts were treated with NIL 300 mg once daily (qd). At the end of consolidation phase, pts with sDMR entered TFR phase and discontinued NIL; indeed, pts with at least major molecular response (MMR; BCR-ABL ≤0.1% IS), but without sDMR, continued NIL 300 mg qd. At any time, pts with loss of MMR returned to NIL 300 mg bid. During TFR phase, BCR-ABL levels were monitored monthly from wk 52-96, and then every 3 months. Pts on half-dose or full-dose NIL were monitored every 3 months. The primary endpoint is the percentage of pts in full treatment-free remission (FTFR) 96 wks after the start of consolidation phase. FTFR is defined as pts with MMR or better, including those who remained in discontinuation during TFR phase and those who are treated with half the standard dose. Key secondary endpoints include percentage of pts with sDMR at wk 48; TFR rate at wk 96 and 144; BCR-ABL kinetics and safety. The predictive role of digital droplet PCR is also evaluated as an exploratory objective. Results: Overall, 113 pts were screened and 107 entered consolidation phase. This interim analysis included 52 pts who reached the end of consolidation phase by data cut-off period (February 8, 2021). Of these 52 pts, 49 (94.2%) were ongoing by data cut-off and 3 (5.8%) discontinued the study (1 patient due to adverse event (AE) and 2 per patient's decision). Median age at study entry was 49.5 years. Median time from diagnosis was 5.6 years and median dose of prior NIL treatment was 600 mg/day for all pts except one who was on NIL 450 mg/day at baseline. Median duration of last sustained MR4 and MR4.5 were 30 and 16.5 months, respectively. Further details are listed in Table 1. At screening, molecular response categories were MR4.0 in 13.7%, MR4.5 in 23.1% and undetectable MR4.5 in 63.5% of pts. During consolidation phase, 5 (9.6%) pts discontinued prematurely: 2 pts restarted NIL full dose (3.8%) for MMR loss, 2 (3.8%) discontinued for AEs and 1 (1.9%) for pt decision. Overall, 47 pts completed consolidation: of them 40 (76.9%) sustained DMR and 7 (13.5%) maintained MMR but not sDMR. Of the 7 pts not sustaining DMR during consolidation, 6 regained DMR after a median of 4.4 months, while 1 pt was still in MMR by data cutoff. The 2 pts who lost MMR after 5 and 8 months regained MMR and 1 regained DMR by data cutoff after increasing NIL to 300 mg bid. Median time spent in consolidation phase was 11.7 months, and the evolution of response categories over time is shown in Figure 1. During consolidation phase, AEs were observed in 16 pts (30.8%), of them 2 (3.8%) pts had serious AEs: 1 patient had skin ulcers and COVID-19 related pneumonia, while 1 patient had unstable angina. No deaths and disease progressions were observed. Conclusions: DANTE is the first study that showed the safety and feasibility of NIL de-escalation before TFR in CML-CP pts with sDMR. Interim results suggest that loss of MMR during de-escalation is rare. De-escalation strategy may lead to further improvement of TFR outcome and tolerability and may also preemptively support the identification of pts who may not be ready for discontinuation, with a tailored approach. To date, accuracy in predicting TFR outcome is still low, and the de-escalation setting may sharpen biological and clinical predictive factors, including the potential role of digital PCR. Figure 1 Figure 1. Disclosures Breccia: Abbvie: Honoraria; Pfizer: Honoraria; Novartis: Honoraria; Incyte: Honoraria; Bristol Myers Squibb/Celgene: Honoraria. Abruzzese: Incyte: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria. Stagno: InCyte: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Other: Support for attending meetings and/or travel; Novartis: Consultancy, Honoraria, Other: Support for attending meetings and/or travel, Research Funding. Iurlo: Incyte: Speakers Bureau; Novartis: Speakers Bureau; Pfizer: Speakers Bureau; Bristol Myers Squibb: Speakers Bureau. Sportoletti: AstraZeneca: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria. Lemoli: Jazz, Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie, Daiichi Sankyo, Servier: Honoraria, Speakers Bureau; Celgene: Other: Support for attending meetings and/or travel. Siragusa: Novartis, CSL, Behring, Amgen, Novonoridsk, SOBI, Bayer: Consultancy, Honoraria, Speakers Bureau. Chiodi: Novartis: Current Employment.

Predictive Value Of Early Molecular Responses In Outcomes Of Patients With Chronic Myeloid Leukemia Treated With Imatinib In First-Line Therapy

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4941-4941
Author(s):  
Katia B. Pagnano ◽  
Bruna Vergilio ◽  
Eliana C M Miranda ◽  
Marcia Torresan Delamain ◽  
Maria Helena De Almeida ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Cytogenetic Response ◽  
Molecular Response ◽  
First Line ◽  
Molecular Responses ◽  
Advanced Phase ◽  
Significant Difference ◽  
The Impact

Abstract Several studies demonstrated the prognostic significance of an early molecular response in chronic myeloid leukemia (CML) patients (pts) treated with imatinib in first line or other tyrosine kinase inhibitors. Aims: The aim of this study was to evaluate the impact of early molecular responses, at 3 and 6 months after treatment with imatinib in CML pts and correlate these responses with CCR, MMR, overall survival (OS) and event free survival (EFS). Patients and Methods Between February 2006 and June 2012, 95  adult pts with newly diagnosed CML in chronic phase (CP) received imatinib 400mg/daily. CP was defined using WHO 2008 criteria. All pts received a short course of hydroxiurea until imatinib was available. Cytogenetic analysis was performed at diagnosis, 3, 6, 12 and 18 months after starting therapy and then every 12-24 months thereafter. BCR-ABL transcripts were measured in peripheral blood at 3-month intervals using quantitative RT-PCR (RQ-PCR). Results were expressed as BCR-ABL/ABL ratio, with conversion to the international scale (IS). Major molecular response (MMR) was defined as a transcript level ≤ 0.1% (IS). Statistical analysis: OS was measured from imatinib start until date of death or last visit. An event was defined as death from any cause. EFS was measured from imatinib start until the first event (loss of complete hematological response (CHR); complete cytogenetic response (CCR), progression to advanced phase, death or imatinib discontinuation) or last visit. OS and EFS rates were calculated using Kaplan-Meier method and log-rank test to compare its curves. The MMR probabilities according to molecular responses at 3 and 6 months were calculated by c2 method and cumulative incidence, considering as competitive event death or progression, before the event. Results 95 pts were analyzed, 57 (60%) male, with a median age of 47 years (17-79); Sokal score: high, intermediate and low was 30, 38.6 and 31.4% respectively; EUTOS scores was 81.5% low and 18.5% high. The median time from diagnosis until imatinib therapy was 1 month (0-5) and the follow-up was 39 month (3-89). Responses: 88% achieved CHR; 50% CCR and 53% MMR. One patient progressed to advanced phase during follow-up, while on imatinib treatment. 21 (22%) pts discontinued imatinib due to intolerance (47.6%); resistance (42.9%), death (4.8%) and Allo-HSCT (4.8%). At 3 months from the start of therapy, 30/64 (46.8%) achieved CCR, 15/64 (23.4%) partial cytogenetic response and 20/64 (31.2%) less than partial; by RQ-PCR, 72.3% (68/94) achieved at 3 months BCR-ABL transcripts ≤10% and 27.7% (26/94) > 10%. At 6 months 55.2% (48/87) had BCR-ABL transcripts ≤ 1% and 44.8% (39/87) >1%. The OS was 97% (95%CI: 95-99%) and EFS 63% (95%CI: 52-75%).There was no significant difference in OS and EFS in pts with RQ-PCR > 10% vs ≤ 10% at 3 months (figure 1), but pts with BCR-ABL transcripts > 10 and >1-10% at 6 months had an inferior EFS in comparison with pts with  BCR-ABL transcripts ≤ 1%  (41%,50%,89% respectively - p= 0.005), (figure 2). The CI showed that CCR pts at 3 months reached MMR earlier at 24 month (54% vs 18%, p=0.03), as well as CCR pts at 6 months, albeit no significance statistically (52% vs 37%, p= 0.16). For RQ-PCR at 3 months, pts with BCR-ABL transcripts 0-1% had a probability of 88% to achieve MMR, 1-10% had 52% and >10% 42%, p< 0.0001 (figure 3). In conclusion, our results show that early molecular responses are predictive of achieving MMR and BCR-ABL transcripts <1% at 6 months is predictive of EFS in CP-CML treated with imatinib. Disclosures: No relevant conflicts of interest to declare.

Two-Year Consolidation By Nilotinib Is Associated with Successful Treatment Free Remission in Chronic Myeloid Leukemia with MR4.5: Subgroup Analysis from STAT2 Trial in Japan

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 1889-1889 ◽  
Author(s):  
Naoto Takahashi ◽  
Chiaki Nakaseko ◽  
Kaichi Nishiwaki ◽  
Hisashi Wakita
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Subgroup Analysis ◽  
Myeloid Leukemia ◽  
Research Funding ◽  
Second Generation ◽  
Second Line ◽  
First Line ◽  
Prior Therapy ◽  
Line Therapy ◽  
Treatment Free Remission

Abstract Background Nilotinib (NIL) is a second-generation tyrosine kinase inhibitor (TKI) that exhibits significant efficacy as first- or second-line treatment in patients with chronic myeloid leukemia (CML). Superior rates of deeper molecular responses (DMR) were achieved with NIL vs. imatinib (IM) in patients newly diagnosed with CML in chronic phase (CML-CP) in the ENESTnd trial. In addition, the ENESTcmr study demonstrated that switching to NIL after a minimum of 2 years on IM led to increased rates of DMR vs. remaining on IM. Switching to NIL treatment for 2 years safely led to MR4,5 (BCR-ABLIS…0.0032%) in 47.5% of patients with major molecular response (MMR) on long-term IM therapy in our STAT1 trial. Recently, treatment free remission (TFR) was proposed as one of the goals in CML treatment. Indeed, prospective trials suggest that IM therapy may be safely and successfully discontinued in 40% of CML patients with MR4.5. STAT2 is the first study to evaluate the efficacy of two-year consolidation by NIL for successful TFR in patients with CML-CP who had achieved MR4.5. Before enrolling in STAT2, some patients were treated by not only IM but also NIL because of MMR but no MR4.5 after IM therapy, and some patients changed over from STAT1 to STAT2. Here, we present the results of the subgroup analysis from STAT2 based on the prior treatments at the time of entry into the study. Methods In the STAT2 trial, patients who achieved MR4.5 on IM front line therapy (subgroup 1; SG1) or NIL second line therapy after IM therapy (subgroup 2; SG2) were eligible and NIL was given twice daily at the dose of 600 mg/day for 2 years in consolidation phase. The primary endpoint of STAT2 was the proportion of patients with successful TFR, defined as no confirmed loss of MR4.5 (2 consecutive IS RQ-PCR tests), within the first 12 months of TFR phase. Thirty-five institutions in STAT study group participated. The study was conducted in accordance with the principles of the Declaration of Helsinki. Informed consent was signed by all patients according to institutional guidelines. The study was approved by all institutional review boards and registered with UMIN-CTR (000005904). Results Between July 2011 and December 2012, 96 patients were enrolled in STAT2. Among 96 patients, 50 patients were treated by IM first line only as prior therapy (SG1). On the other hand, 40 patients were treated by IM first line and NIL second line including 21 patients who changed over from STAT1 to STAT2 because they achieved MR4.5 (SG2). Six patients were excluded in this analysis because second generation TKIs were taken as a first line therapy. Among patients treated by NIL for 2 years in this study, 40/50 (80%; 95% CI, 68.4%-88.7%) in SG1 and 33/40 (82.5%; 95% CI, 69.6%-91.5%) in SG2 entered the TFR phase, respectively. The median age was 54.5 years in SG1 and 56.0 years in SG2. The ratio of men to women was 26:14 in SG1 and 18:15 in SG2. The total duration of TKI treatment was 110 months for the SG1 with a median of 86 months of IM, and 24 months of NIL, and 93 months in SG2 with a median of 62 months of IM, and 31 months of NIL,, respectively. All patients achieved MR4.5 at the time of entry into the study and the median time to MR4.5 was 47 months in SG1 and 60 months in SG2.The proportion of patients who maintained TFR at 12 months after stopping NIL was similar across the 2 subgroups: 25/40 (62.5%; 95% CI, 48.3%-77.3%) in SG1, and 23/33 (69.7%; 95% CI, 54.0%-82.5%) in SG2. The Kaplan-Meier (KM) analysis of TFR survival showed that in the 2 subgroups, the majority of events occurred within the first 6 months after stopping NIL (Figure 1). There were no significant differences between these 2 subgroups. Conclusion After two-year consolidation by NIL of CML-CP patients who achieved MR4.5, the TFR rate was 67.9% (90%CI: 58.2% to 76.6%) at 12 months in the STAT2 trial. In the present analysis looking at the prior TKI exposure, the TFR rate was similar in patients treated with IM first line only or who switched from IM to NIL before entering the study, despite the fact that the treatment duration of switched patients was slightly shorter. These findings suggest that two-year consolidation by NIL is associated with successful TFR in CML with MR4.5 that was achieved with IM alone or after switching to NIL. Figure Kaplan-Meiercurve of TFR survival in the 2 subgroups based onthe prior treatmentsbefore two-year consolidation by NIL, IM first line only as prior therapy (subgroup1) and IM first line and NIL second line (subgroup2). Figure. Kaplan-Meiercurve of TFR survival in the 2 subgroups based onthe prior treatmentsbefore two-year consolidation by NIL, IM first line only as prior therapy (subgroup1) and IM first line and NIL second line (subgroup2). Disclosures Takahashi: PFIZER: Honoraria, Research Funding; BMS: Honoraria; NOVARTIS PHARMA: Honoraria, Research Funding. Nakaseko:BMS: Honoraria, Research Funding; PFIZER: Honoraria, Research Funding; NOVARTIS: Honoraria. Nishiwaki:Novartis PHARMA: Research Funding.

scholarly journals B3a2 Transcript Is an Independent Factor for the Achievement of a Deep Molecular Response in Chronic Phase - Chronic Myeloid Leukemia Patients Treated with Imatinib in First-Line

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 1749-1749 ◽  
Author(s):  
Matheus Sebastian Da Silva ◽  
Eliana C Miranda ◽  
Marcia Torresan Delamain ◽  
Gislaine Oliveira Duarte ◽  
Bruna R Vergilio ◽  
...  
Keyword(s):  
Overall Survival ◽  
Multivariate Analysis ◽  
Chronic Myeloid Leukemia ◽  
Cumulative Incidence ◽  
Myeloid Leukemia ◽  
Molecular Response ◽  
Imatinib Treatment ◽  
Independent Factor ◽  
First Line ◽  
Molecular Responses

Abstract Introduction: The achievement of a deep and sustained molecular response after treatment with tyrosine kinase inhibitors (TKI) is one of the requirements for therapy discontinuation in chronic myeloid leukemia (CML) patients. Objectives: This study aimed to evaluate the proportion of CML patients treated with imatinib in first-line that achieve MR4.5 (BCR-ABL transcripts ≤ 0.0032% in the international scale) after imatinib treatment and the predictive factors for this response. The secondary objectives were to evaluate the rate of MMR (PCR ≤0.1%), MR4.0 (PCR ≤ 0.01%), time to molecular responses, event-free survival, progression-free and overall survival. Patients and methods: This is a retrospective analysis of CP-CML patients treated in first-line with imatinib in a single center. Patients diagnosed after 2006 were managed according to the European Leukemia Net recommendations. All patients started CML imatinib within six months from diagnosis. The type of BCR-ABL1 transcript was determined by multiplex RT-PCR from cDNA synthesized from total leukocytes RNA at diagnosis. BCR-ABL transcripts by quantitative real-time polymerase chain reaction were assessed at baseline, and then every three months for the first year until reaching a stable major molecular response, then every 3-6 months. The SPSS software was used for the Cox Regression model for univariate and multivariate analysis, using backward Wald. The cumulative incidence was calculated with the R Program, with Gray test for curve comparisons. Event-free, progression-free and overall survivals were calculated with the Kaplan-Meier method, and the curves were compared with the log-rank test. Results: From January 2005 to December 2015 172 patients were treated with imatinib, median age 48 years (18-93), 55.8% male. Sokal score: 31% low-risk, 40% intermediate-risk and 29% high-risk. The median follow-up was 56 months (0-157). The Cumulative Incidence (CI) of MMR was 48% in 24 months and 84% in 5 years, while the CI of MR4.0 and MR4.5 was 63% and 51%, respectively, in 5 years. The median time to MMR, MR4.0 and MR4.5 was 16.7 (2-102), 31 (5-150) and 36 months (7-153), respectively. The univariate regression factors related to MR4.5 achievement were: age >48 years (HR 1.79; 95%CI: 1.08-2.98; P=0.023); days between diagnosis and imatinib start (HR=0.99; 95%CI: 0.98-0.99, P=0.020); e14a2 (b3a2) transcript (HR= 3.37; 95%CI: 1.67-6.81; P=0.001), which was the only factor in the multivariate analysis. Imatinib was discontinued in 96/172 (55.8%) patients due to resistance (36.5%), intolerance (20.8%), clinical trials (25%), death (15.6%) and adherence (2.1%). Eighteen out of 67 (26.8%) patients that achieved MR4.5 are currently participating in a discontinuation trial. Overall survival, PFS and EFS were 92%, 87% and 61% in 5 years. Conclusion: Approximately half of the patients that start imatinib in first-line obtain deep molecular responses within five years and could be candidates for treatment discontinuation. B3a2 transcript was an independent factor for MR4.5 achievement in the multivariate analysis, confirming the results of other studies that have reported earlier and deeper molecular responses in patients with b3a2 transcripts. Disclosures De Paula: Hematology and Transfusion Medicine Center, University of Campinas: Employment. Pagnano:Abbvie: Consultancy; EMS: Other: Financial support for participation in congress; Shire: Other: Lecture; Novartis: Consultancy.

scholarly journals Managing chronic myeloid leukemia for treatment-free remission: a proposal from the GIMEMA CML WP

2019 ◽  
Vol 3 (24) ◽  
pp. 4280-4290 ◽  
Author(s):  
Michele Baccarani ◽  
Elisabetta Abruzzese ◽  
Vincenzo Accurso ◽  
Francesco Albano ◽  
Mario Annunziata ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Disease Risk ◽  
Working Party ◽  
Line Treatment ◽  
First Line ◽  
Term Survival ◽  
Treatment Free Remission ◽  
Definition Of ◽  
First Line Treatment

Abstract Several papers authored by international experts have proposed recommendations on the management of BCR-ABL1+ chronic myeloid leukemia (CML). Following these recommendations, survival of CML patients has become very close to normal. The next, ambitious, step is to bring as many patients as possible into a condition of treatment-free remission (TFR). The Gruppo Italiano Malattie EMatologiche dell’Adulto (GIMEMA; Italian Group for Hematologic Diseases of the Adult) CML Working Party (WP) has developed a project aimed at selecting the treatment policies that may increase the probability of TFR, taking into account 4 variables: the need for TFR, the tyrosine kinase inhibitors (TKIs), the characteristics of leukemia, and the patient. A Delphi-like method was used to reach a consensus among the representatives of 50 centers of the CML WP. A consensus was reached on the assessment of disease risk (EUTOS Long Term Survival [ELTS] score), on the definition of the most appropriate age boundaries for the choice of first-line treatment, on the choice of the TKI for first-line treatment, and on the definition of the responses that do not require a change of the TKI (BCR-ABL1 ≤10% at 3 months, ≤1% at 6 months, ≤0.1% at 12 months, ≤0.01% at 24 months), and of the responses that require a change of the TKI, when the goal is TFR (BCR-ABL1 &gt;10% at 3 and 6 months, &gt;1% at 12 months, and &gt;0.1% at 24 months). These suggestions may help optimize the treatment strategy for TFR.

scholarly journals Prognostic Value of Multi-Drug Resistance 1 Gene (MDR1) Expression in Newly Diagnosed Patients with Chronic Myeloid Leukemia on Nilotinib Treatment—a Subanalysis of the ENEST1st Study

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 3144-3144 ◽  
Author(s):  
Christian Dietz ◽  
Michael Lauseker ◽  
Benjamin Hanfstein ◽  
Philippe Rousselot ◽  
Thoralf Lange ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Research Funding ◽  
Chronic Phase ◽  
Multi Drug Resistance ◽  
Newly Diagnosed ◽  
First Line ◽  
Molecular Responses ◽  
Expression Levels ◽  
Mdr1 Expression

Abstract Introduction MDR1 gene expression has recently been reported to be associated with clinical outcome in imatinib-resistant patients with chronic myeloid leukemia (CML) on second-line nilotinib treatment (Agrawal et al., Leukemia 2014). High MDR1 expression was predictive for achieving deeper cytogenetic and molecular responses as well as duration of chronic phase. We thus prospectively evaluated the value of MDR1 expression analysis in the first-line situation within a large European, multicenter trial of CML patients under treatment with nilotinib. Methods 305 patients enrolled on the ENEST1st study (Evaluating Nilotinib Efficacy and Safety in clinical Trials as First-Line Treatment, NCT01061177) consented to participate in this substudy. Of these, 225 patients were evaluable due to sample availability and presence of typical e14a2 and/or e13a2 BCR-ABL1 transcripts. The median age was 52 (range 18-83), 39% were female. Prior to therapy, the expression of MDR1, BCR-ABL1, and GUSB were determined using a serial dilution of a plasmid constructs harboring MDR1 and GUSB and BCR-ABL1 and GUSB sequences. Ratios MDR1/GUSB and BCR-ABL1/GUSB were calculated. ROC curves were established using initial MDR1 and BCR-ABL1 expression levels aiming to achieve the primary endpoint of MR4 (defined as BCR-ABL1 ≤ 0.01% on the International Scale [BCR-ABL1IS] or undetectable BCR-ABL1 in cDNA with ≥ 10,000 ABL1 transcripts) at 18 months or to achieve a MMR (≤ 0.1% BCR-ABL1IS) at 9 months. Mann-Whitney tests have been applied using a significance level of 0.05. Results At 9 months, 161 patients (72%) achieved MMR and at 18 months 111 patients (49%) a MR4. The median ratio MDR1/GUSB among all evaluable patients was 11.4% (range, 0.6-318.1), the median ratio BCR-ABL1/GUSB was 22.2% (range 0.09-198.7). Initial BCR-ABL1/GUSB levels did not predict MMR or MR4 at 9 or 18 months. However, initial ratios MDR1/GUSB were predictive for the achievement of MMR at 9 months (best cut-off 3.8%, sensitivity 88.8%, specificity 26.6%, AUC 0.598, p=0.022) and for reaching MR4 at 18 months (best cut-off 7.90%, sensitivity 72.1%, specificity 51.8%, AUC 0.624, p=0.001). Conclusions High MDR1 expression levels in newly diagnosed CML patients appear to be associated with deeper molecular responses within the first 18 months of nilotinib treatment. These data merit further exploration and if validated would justify the investigation of frontline CML therapy guided by baseline MDR1 expression levels. Disclosures Dietz: Novartis: Research Funding. Hanfstein:Bristol-Myers Squibb: Honoraria; Novartis: Research Funding. Rousselot:Novartis: Research Funding. Lange:Novartis: Consultancy, Honoraria, Research Funding. Maier:Novartis: Research Funding. Foroni:Novartis: Research Funding. Gerrard:Novartis: Research Funding. Talmaci:Novartis: Research Funding. Janssen:Novartis: Research Funding. Frank:Novartis: Employment. Saussele:Pfizer: Honoraria, Travel, Travel Other; Bristol-Myers Squibb: Honoraria, Research Funding, Travel, Travel Other; Novartis: Honoraria, Research Funding, Travel Other. Giles:Novartis: Honoraria, Research Funding. Hochhaus:Novartis: Research Funding. Müller:Novartis: Honoraria, Research Funding.

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