Abstract: Abstract 357 Treatment of CML with imatinib of 400 mg can be unsatisfactory. Treatment optimization is warranted. The German CML-Study group has therefore conducted a randomized study comparing imatinib 800 mg vs 400 mg vs 400 mg + IFN. A significantly faster achievement of MMR at 12 months has been observed with imatinib 800 mg in a tolerability adapted manner and MMR by 12 months has been found to translate into better overall survival. Since stable CMR has been associated with durable off-treatment remissions we sought to analyse the impact of tolerability-adapted imatinib 800 mg on CMR and survival. Standardized determinations of molecular response and evaluation of its impact on outcome are goals of CML-Study IV. CMR4 is defined as a BCR-ABL/ABL ratio of 〈 0,01 on the International Scale. From July 2002 – April 30, 2009 1022 newly diagnosed patients with CML in chronic phase were randomized, 1012 were evaluable (338 with imatinib 800 mg, 324 with imatinib 400 mg, 350 with imatinib plus IFN). Median observation time was 40 months. The median average daily imatinib doses were 628 mg in the 800 mg arm and 400 mg in the 400 mg based arms. The actual median daily doses in the 800 mg arm per 3-months periods were: 555 mg, 737 mg, 613 mg, 600 mg, and 600 mg thereafter, reflecting the run–in period with imatinib 400 mg for 6 weeks in the first period and the adaptation to tolerability from the third 3-months period onwards. Median daily imatinib doses in the 400 mg arms were 400 mg throughout. Adaptation of imatinib dose in the 800 mg arm according to tolerability is reflected by similar higher-grade adverse events rates (WHO grades 3 and 4) with all treatments. Significantly higher remission rates were achieved with imatinib 800 mg by 12 months. The cumulative incidences of CCR by 12 months were 63% [95%CI:56.4-67.9] with imatinib 800 mg vs 50% [95%CI:43.0-54.5] with the two 400 mg arms. The cumulative incidences of MMR by 12 months were 54.8% [95%CI:48.7-59.7] with imatinib 800 mg vs 30.8% [95%CI:26.6-36.1] with imatinib 400 mg vs 34.7% [95%CI:29.0-39.2] with imatinib + IFN. The cumulative incidences of CMR4 compared with the MMR incidences over the first 36 months are shown in Table 1. Imatinib 800 mg shows superior CMR4 rates over the entire 36 months period, CMR4 is reached significantly faster with imatinib 800 mg as compared to the 400 mg arms. The CMR4 rates reach 56.8% by 36 months [95%CI:49.4-63.5] as compared to 45.5% with imatinib 400 mg [95%CI:38.7-51.0] and 40.5% with imatinib plus IFN [95%CI:34.6-46.3] . Most patients have stable CMR4 over the entire period. Time after start of treat-ment (months) Cumulative incidences MMR(%) CMR4 (%) IM400 n=306 D IM800 n=328 D IM400 +IFN n=336 IM400 n=306 D IM800 n=328 D IM400 +IFN n=336 6 8.6 9.5 18.1 9.7 8.4 3 0.7 3.7 1.3 2.4 12 30.8 24.0 54.8 20.1 34.7 7.5 12.3 19.8 7.4 12.4 18 50.3 18.1 68.4 14.3 54.1 21.2 12.2 33.4 9.8 23.6 24 63 13.0 76.0 13.2 62.8 30.7 12.3 43 13 30.0 36 79.3 2.3 81.6 10.9 70.7 45.5 11.3 56.8 16.3 40.5 In summary, superior CMR4 rates are achieved with high-dose imatinib adapted to good tolerability, and more patients in the tolerability-adapted 800 mg arm have stable CMR4 qualifying for treatment discontinuation as compared to the 400 mg based arms. With improved application imatinib remains first choice for early CML. Disclosures: Koschmieder: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. German CML-Study Group:Deutsche Krebshilfe: Research Funding; Novartis: Research Funding; Roche: Research Funding; BMBF: Research Funding; Essex: Research Funding.

Abstract: Background: In the current ELN recommendations (Baccarani et al., Blood 2013) the optimal time point to achieve major molecular remission (MMR) is defined at 12 months after diagnosis of CML. MMR is not a failure criterion at any time point leading to uncertainties when to change therapy in CML patients not reaching MMR after 12 months. Aims: We sought to evaluate a failure time point for MMR using data of the CML-Study IV, a randomized five-arm trial designed to optimize imatinib therapy alone or in combination. In addition the optimal time-point to achieve a MMR should be evaluated. Methods: Patients with valid molecular analysis on MR4 level were divided randomly into a learning (LS) and a validation sample (VS). For the LS, MR2 (defined as BCR-ABL 〈 1% which corresponds to complete cytogenetic remission (Lauseker et al. 2014)), MMR and deep molecular remission levels (MR4 or deeper) monthly landmarks were defined between one and five years after diagnosis. A patient was considered to be in MR2, MMR or MR4 from the first diagnosis of the corresponding remission level and could only change to a higher level of response. Patients were censored after SCT. The best prediction time was found via dynamic prediction by landmarking (van Houwelingen, Scand J Stat 2007). For the failure time point analysis, for each of the resulting 48 landmarks, a Cox model was used to define the time to progression with age and EUTOS score as additional prognostic factors. Additionally, the regression coefficients of the model of one landmark were converted to hazard ratios (HR) and treated as dependent on the HRs of the other landmarks, using a cubic smoothing function (see Fig 1). The minimum of this function was considered to be the optimal landmark point for the prediction of progression-free survival (PFS). For the calculated time point, landmark analysis for probability of PFS (defined as appearance of accelerated phase, blast crisis or death) was performed in the VS. For the evaluation of the optimal time point of achieving a MMR the same analysis was done from 0.25 to 5 years to define the time to MR4 or deeper. Results: 1551 patients were randomized from 2002 to 2012, 1358 had a valid molecular analysis on the MR4 level. 114 patients in the imatinib after IFN arm and 16 patients with missing EUTOS score were excluded. Of the 1228 evaluable patients two thirds were randomly allocated to the LS (n=818) and one third to the VS (n=410). Percentage of patients of the LS in MR2, MMR and MR4 or deeper at one year was 28%, 29% and 14%, and at 5 years 5%, 21% and 71%, respectively. Monthly time points in between were also calculated. 44 patients of the LS reached MMR on second generation tyrosine kinase inhibitors.. The minimum of the cubic function of the HRs was found for MMR at 2.34 years with a HR of 0.25 (compared to patients without any remission) and 0.75 compared to those in MR2. For MR4 or deeper no exact time point could be calculated (see Fig. 1), although it was shown that the risk of progression was slightly lower for MR4 than for MMR. Since the time interval for molecular evaluation in the study is 3 months, the validation was done with 2.25 instead of 2.34 years. 364 of the 410 of the VS were still at risk at this time point and evaluable. A significant PFS advantage for patients in MMR could be demonstrated (p=0.018). At 8 years, the probability of PFS for patients in MMR was 90.8% (confidence interval 87.0-93.7%) vs. 80.5% (confidence interval 70.2-88.6%) for patients not in MMR (see Fig 2). For the optimal MMR analysis no singular time point could be calculated as the earlier a MMR was reached the higher was the chance to achieve a MR4. Conclusions: In this model, an optimal time point to predict PFS in patients with MMR was defined at 2.25 years after diagnosis and could be validated as significant. Nevertheless, patients being in MMR had a lower risk of progression than patients not being in MMR on any other time point as well. With this model we can give hints when to define MMR as failure and a change in therapy should be considered. Despite this we should keep in mind that the earlier MMR was achieved the higher was the chance to achieve deep molecular response later during therapy. Figure 1 Cubic smoothing function of the HR to predict PFS with confidence intervals Figure 1. Cubic smoothing function of the HR to predict PFS with confidence intervals Figure 2 Landmark analysis at 2.25 years for PFS of the VS Figure 2. Landmark analysis at 2.25 years for PFS of the VS Disclosures Saussele: Novartis: Honoraria, Research Funding, Travel Other; Bristol-Myers Squibb: Honoraria, Research Funding, Travel, Travel Other; Pfizer: Honoraria, Travel, Travel Other. Hehlmann:Bristol-Myers Squibb: Research Funding; Novartis: Research Funding. Schnittger:MLL Munich Leukemia Laboratory: Equity Ownership. Hanfstein:Novartis: Research Funding; Bristol-Myers Squibb: Honoraria. Neubauer:MedUpdate: Honoraria, Speakers Bureau. Kneba:Novartis: Consultancy, Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Pfirrmann:Novartis: Consultancy; Bristol-Myers Squibb: Honoraria. Hochhaus:Novartis: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; ARIAD: Honoraria, Research Funding; Pfizer: Consultancy, Research Funding. Müller:Novartis: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; ARIAD: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding.

Abstract: Abstract 67 Dose optimized imatinib (IM) at doses of 400– 800mg has been shown to induce faster and deeper cytogenetic and molecular – responses than standard IM (400mg/day). Since complete molecular remission (CMR 4.5) identifies a subgroup of patients who may stay in remission even after discontinuation of treatment, it was of interest to analyse whether CMR 4.5 is reached faster with dose optimized IM and whether CMR 4.5 correlates with survival. CMR 4 and CMR 4.5 are defined as ≤ 0.01% BCR-ABL IS or ≥ 4. log reduction and ≤ 0.0032% BCR-ABL IS or ≥ 4.5 log reduction, respectively, from IRIS baseline as determined by real-time PCR. CML-Study IV is a five arm randomized study of IM 400 mg vs IM 400 mg + IFN vs. IM 400 mg + Ara C vs. IM after IFN failure vs. IM 800 mg. In the IM 800 arm, a 6 weeks run in period at IM 400 mg was followed by a dose increase to 800 mg and then by a dose reduction according to tolerability. Grade 3 or 4 adverse effects (AE) were to be avoided. From July 2002 to March 2012 a total of 1551 patients with newly diagnosed chronic phase CML were randomized of whom 1525 were evaluable. Median age was 52 years, 88% were EUTOS low risk, 12% high risk, 36% were Euro score low risk, 52% intermediate and 12% high risk, 38% were Sokal low risk, 38% intermediate and 24% high risk. 113 patients were transplanted, 246 received 2nd generation TKI. 152 patients have died, 90 of CML or unknown reasons, 62 of not directly CML-related causes. After a median observation time of 67,5 months 6 years OS was 88.2% and PFS 85.6%. CCR, MMR, CMR 4 and CMR 4,5 were achieved significantly faster with dose optimized IM (400 – 800 mg). No significant differences in remission rates were observed between IM 400 mg and the combination arms IM 400 mg + IFN and IM 400 mg + Ara C, whereas IM after IFN failure thus far yielded significantly slower response rates. After 4 years CCR rates were for IM 400, IM 400 + IFN, IM 400 + Ara C, IM 400 after IFN, and IM 800, 80%, 75%, 73%, 59% and 80%, respectively, MMR rates 84%, 77%, 82%, 61% and 88%, CMR 4 rates 57%, 55%, 55%, 40% and 65%, and CMR 4.5 rates 40%,42%, 42%, 28% and 52%, respectively. CMR 4 was reached after a median of 27 months with IM 800 and 41.5 months with IM 400. CMR 4.5 was reached after a median of 41.5 months with IM 800 and 63 months with IM 400. EUTOS low risk patients reached all remissions faster than EUTOS high risk patients. The differences of CMR 4 rates between IM 800 and IM 400 at 3 years were 13% and at 4 years 8%, and of CMR 4.5 rates at 3 years 10% and at 4 years 13%. Grade 3 and 4 AE were not different between IM 400 and dose optimized IM 800. Independent of treatment approach, CMR 4 and more clearly CMR 4.5 at 3 years predicted better OS and PFS, if compared with patients without CMR 4 or CMR 4.5, respectively. CMR 4 and 4.5 were stable. After a median duration of CMR 4 of 3.7 years only 4 of 792 patients with CMR 4 have progressed. Life expectancy with CMR 4 and 4.5 was identical to that of the age matched population. We conclude that dose optimized IM induces CMR 4.5 faster than IM 400 and that CMR 4 and CMR 4.5 at 3 years are associated with a survival advantage. Dose optimized IM may provide an improved therapeutic basis for unmaintained treatment discontinuation in patients with CML. Disclosures: Hehlmann: Novartis: Research Funding. Müller:Novartis, BMS: Consultancy, Honoraria, Research Funding. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Equity Ownership. Hochhaus:Novartis, BMS, MSD, Ariad, Pfizer: Consultancy Other, Honoraria, Research Funding.

Abstract: 7051 Background: Since complete molecular remission (CMR 4.5) defines a subgroup of patients who may stay in remission even after discontinuation of treatment, we analysed whether CMR 4.5 is reached faster with dose optimized IM 800 mg and whether the achievement of CMR 4.5 at specified points in time results in better survival than the achievement of less deep remissions. Methods: Confirmed CMR 4 and CMR 4.5 are defined as ≤ 0.01% BCR-ABL IS or ≥ 4 log reduction and ≤ 0.0032% BCR-ABL IS or ≥ 4.5 log reduction, respectively, from standardized baseline as determined by real-time PCR in 2 independent analyses. Details on CML-Study IV have been published (Hehlmann et al., JCO 2011). Cumulative incidences were estimated under consideration of competing risks. Landmark analyses were performed to evaluate the prognostic impact of different remissions at 4 years on survival. Results: Of 1551 randomized patients with newly diagnosed chronic phase CML 1525 were evaluable. Median age was 52 years, 88% were EUTOS low risk, 12% high risk. 113 patients were transplanted (73 in first chronic phase), 246 received 2nd generation TKI. 152 patients have died. After a median observation time of 67.5 months, 6-year OS was 88.2%.CMR 4.5 was reached after a median of about 76.1 months with IM 800 and 107.3 months with IM 400. EUTOS low-risk patients reached all remissions faster than high-risk patients. Independent of treatment approach CMR 4.5 at 4 years predicted OS significantly better than complete cytogenetic remission (p=0.043), but not significantly better than major molecular remission (MMR) or CMR4. After a median observation of 3.9 years 1 of 626 patients with CMR 4 has progressed. Only six of the 394 patients with CMR 4.5 have died after a median observation time of 3.0 years, no patient has progressed. An additional finding was that achieving MMR at 3 and at 6 months predicts faster achievement of CMR 4.5. Conclusions: We conclude that dose optimized IM 800 induces CMR 4.5 faster than IM 400 and that CMR 4.5 at 4 years is associated with a survival advantage. Dose optimized IM 800 may provide an improved therapeutic basis for treatment discontinuation in patients with CML. Clinical trial information: NCT00055874.

Abstract: Deep molecular response (MR 4.5 ) defines a subgroup of patients with chronic myeloid leukemia (CML) who may stay in unmaintained remission after treatment discontinuation. It is unclear how many patients achieve MR 4.5 under different treatment modalities and whether MR 4.5 predicts survival. Patients and Methods Patients from the randomized CML-Study IV were analyzed for confirmed MR 4.5 which was defined as ≥ 4.5 log reduction of BCR-ABL on the international scale (IS) and determined by reverse transcriptase polymerase chain reaction in two consecutive analyses. Landmark analyses were performed to assess the impact of MR 4.5 on survival. Results Of 1,551 randomly assigned patients, 1,524 were assessable. After a median observation time of 67.5 months, 5-year overall survival (OS) was 90%, 5-year progression-free-survival was 87.5%, and 8-year OS was 86%. The cumulative incidence of MR 4.5 after 9 years was 70% (median, 4.9 years); confirmed MR 4.5 was 54%. MR 4.5 was reached more quickly with optimized high-dose imatinib than with imatinib 400 mg/day (P = .016). Independent of treatment approach, confirmed MR 4.5 at 4 years predicted significantly higher survival probabilities than 0.1% to 1% IS, which corresponds to complete cytogenetic remission (8-year OS, 92% v 83%; P = .047). High-dose imatinib and early major molecular remission predicted MR 4.5 . No patient with confirmed MR 4.5 has experienced progression. Conclusion MR 4.5 is a new molecular predictor of long-term outcome, is reached by a majority of patients treated with imatinib, and is achieved more quickly with optimized high-dose imatinib, which may provide an improved therapeutic basis for treatment discontinuation in CML.

Abstract: Depth of molecular remission on tyrosine kinase inhibitor (TKI) treatment is of rising importance for chronic myeloid leukemia (CML) patients (pts) with regard to possible treatment discontinuation and competing TKIs available to improve molecular response. At present, it is unknown which level of deep molecular response is necessary for optimal prognosis and for successfully stopping therapy. The aim of this work is both to evaluate the technical feasibility of molecular monitoring at the mentioned level and to search for factors allowing to predict MR5.0 in pts on imatinib (IM)-based treatment. Methods Real-time quantitative PCR on mRNA BCR-ABL transcripts in addition to total ABL transcripts as internal control has been performed on a LightCycler platform in 1,442 pts within the randomized CML-Study IV and adapted according to the International Scale (IS). In order to qualify for MR5.0 the BCR-ABLIS expression should meet one of the following criteria: a positive result ≤0.001% or a negative result with a minimum sample quality of 100,000 ABL copies (Cross et al., Leukemia 2012). Calculating cumulative incidences of remission or progression, the competing risks progression and/or death before possible progression were considered. Cox models were estimated for the multivariate analysis. Results In 1,198 of the 1,442 molecularly examined pts at least one sample fulfilled the sensitivity criteria for a MR5.0 (8,266 of 24,101 samples, 34.3%). Cumulative incidence of MR5.0 was 51% at 8 years. The median time to MR5.0 according to randomized treatment arms differed as follows: IM 800mg 79.7 months (mos), IM 400mg 95.0 mos, IM 400mg + IFNα 98.0 mos, IM 400mg + AraC 103.3 mos, IM 400mg after IFN failure 112.9 mos. A Cox model examining the different treatment arms compared to IM 400mg revealed a significantly higher chance for MR5.0 in the IM 800mg arm (HR 1.305, 95% CI 1.003-1.698, p=0.048). Baseline factors like thrombocytosis 〉 450/nl were associated with better responses (HR 1.701 compared to 〈 450/nl, 95% CI 1.405-2.059, p 〈 0.001) and higher leukocyte counts 〉 100/nl (HR 0.503 compared to 〈 50/nl, 95% CI 0.400-0.632, p 〈 0.001) and 50-100/nl (HR 0.746 compared to 〈 50/nl, 95% CI 0.591-0.942, p=0.014) with unfavorable responses. Other upfront factors like age, gender, blasts, eosinophils, hemoglobin, and EUTOS score did not significantly influence the probability for MR5.0. Taken all treatment arms together, our analyses have shown that the chance of achieving a MR5.0 by 8 years was considerably reduced if the pts had a BCR-ABLIS 〉 10% at 3 mos (40.2% vs 58.0%), 〉 1% at 6 mos (40.3% vs 68.7%), 〉 0.1% at 12 mos (37.7% vs 72.0%), and 〉 0.1% at 24 mos (21.5% vs 60.5%). Conclusion This evaluation of a large randomized trial reveals feasibility of MR5.0 detection in the majority of pts underlining the benefits of standardized molecular monitoring on the IS with optimized highly sensitive technologies. Baseline low leukocyte count, high thrombocyte count and high dose IM treatment are predictors of future MR5.0. Further, early molecular landmarks qualify for excellent outcome giving hope to a rising number of pts to successfully discontinue treatment and avoid possible side effects or comorbidities. Disclosures: Müller: Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Ariad: Consultancy, Honoraria, Research Funding. Hehlmann:BMS: Consultancy, Research Funding; Novartis: Research Funding. Hochhaus:Novartis: Consultancy, Honoraria, Research Funding, Travel Other; BMS: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria; Ariad: Consultancy, Honoraria. Saussele:Novartis: Honoraria, Research Funding, Travel Other; BMS: Honoraria, Research Funding, Travel, Travel Other; Pfizer: Honoraria.

Abstract: Introduction: The clonal selection of a mutant BCR-ABL positive clone can be observed in about one of two patients with imatinib-resistant chronic myeloid leukemia (CML). The early detection of BCR-ABL kinase domain mutations is crucial, since it allows to change the tyrosine kinase inhibitor (TKI) regimen in a timely manner and may therefore prevent disease progression and the accumulation of further genetic lesions. European LeukemiaNet (ELN) recommendations suggest a mutation analysis if optimal response criteria are not achieved at 3, 6, 12 or 18 months, or whenever a loss of optimal response occurs (Soverini et al., Blood 2011). Several attempts have been made to derive this indication from a specific increase of BCR-ABL levels. Here we report on the correlation of a rise in BCR-ABL transcript levels and the prevalence of BCR-ABL kinase domain mutations in imatinib-treated patients of the CML-Study IV. Methods: A total of 1,173 patients were enrolled until 2009 and randomized to one of four imatinib-based treatment arms. BCR-ABLIS of 988 patients was determined in 7,876 samples by quantitative RT-PCR in the central laboratory (median sample number per patient: 8.4, range 1-37; median follow up: 34 months, range 0-86), representing the eligible patients for the study. Thereby, the estimated intra-laboratory variance is assumed to be about 20%. A first rise of BCR-ABLIS to at least two-fold and 〉 0.1% between two samples of a patient's molecular course defined a sample suspected of bearing a mutant BCR-ABL positive clone. A mutation analysis was performed on this critical sample by direct sequencing of ABL exons 4 to 10. Results: A critical rise in BCR-ABLIS was observed in 231 of 988 patients (23%) after a median of 15.2 months on treatment (range 2.8-59.4). In the corresponding sample 33 mutant clones could be detected in 31 patients (13%). Thereby a steeper rise of BCR-ABLIS was correlated with a higher incidence of BCR-ABL mutations in the respective group (table). A total of 18 different mutations could be detected, the most frequent were: M244V, n=7 (21%); E255K, n=4 (12%); T315I, n=3 (9%); L248V, G250E, L387M and F486S, n=2 (6%), respectively. Mutations occur in a substantial proportion (8%) of patients with an only 2 to 3-fold rise of BCR-ABLIS transcript levels (table). Therefore, the most sensitive cut-off should be applied and mutation analysis may be triggered by a doubling of BCR-ABL transcripts at levels 〉 0.1% IS. Conclusion: BCR-ABL kinase domain mutations occur already in a substantial proportion of patients with a doubling of BCR-ABL transcript levels, which should determine mutation analysis. Table 1. Rise of BCR-ABL expression Patients (n) Patients with BCR-ABL mutations (n) Patients with BCR-ABL mutations (%) Inter-sample interval(median, days) 2 to 3-fold 72 6 8.3 98 3 to 5-fold 50 3 6.0 100 5 to 10-fold 39 4 10.3 99 10 to 100-fold 49 10 20.4 98 〉 100-fold 21 8 38.1 125 〉 2-fold (total) 231 31 13.4 101 Disclosures Hanfstein: Novartis: Research Funding; Bristol-Myers Squibb: Honoraria. Hehlmann:Novartis: Research Funding; Bristol-Myers Squibb: Research Funding. Saussele:Novartis: Honoraria, Research Funding, Travel Other; Bristol-Myers Squibb: Honoraria, Research Funding, Travel, Travel Other; Pfizer: Honoraria, Travel, Travel Other. Schnittger:MLL Munich Leukemia Laboratory: Equity Ownership. Neubauer:MedUpdate: Honoraria, Speakers Bureau. Kneba:Novartis: Consultancy, Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Pfirrmann:Novartis: Consultancy; Bristol-Myers Squibb: Honoraria. Hochhaus:Pfizer: Consultancy, Research Funding; ARIAD: Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding. Müller:Novartis: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; ARIAD: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding.

Abstract: Abstract 3761 Introduction: Early assessment of molecular and cytogenetic response at 3 months of imatinib treatment has been shown to predict survival and might trigger treatment intensification in slow responders who are supposed to harbor a BCR-ABL positive clone with inferior susceptibility to tyrosine kinase inhibition (Hanfstein et al., Leukemia 2012). BCR-ABL transcript levels at 3 months depend on levels at diagnosis and the subsequent decline under treatment. Which of both parameters determines the clinical course and allows for prediction of survival is unclear. The BCR-ABL/ABL ratio is supposed to be skewed for high values, e.g. 〉 10%, due to the fact that ABL transcripts are also amplified from the fusion gene and in fact BCR-ABL/(ABL + BCR-ABL) is determined. Therefore, Beta-glucuronidase (GUS) was used as reference gene to determine high transcript levels at diagnosis. In addition, the linearity of the BCR-ABL/GUS scale allowed for an optimization of prognostic cut-off levels. We compared the significance of 1) BCR-ABL/GUS at diagnosis, 2) BCR-ABL/GUS at 3 months, 3) the individual reduction of transcripts given by (BCR-ABL/GUS at 3 months)/(BCR-ABL/GUS at diagnosis), and 4) the established 10% BCR-ABL/ABL landmark expressed on the international scale (BCR-ABLIS). Patients and methods: A total of 337 patients (pts) were investigated. According to the protocol of the German CML study IV pts could have been pre-treated with imatinib up to 6 weeks before randomization. 56 pts with imatinib onset before initial blood sampling within the study were excluded from the analysis. A total of 281 evaluable patients (median age 51 years, range 17–85, 42% female) were treated with an imatinib-based therapy consisting of imatinib 400 mg/d (n=76), imatinib 800 mg/d (n=110) and combinations of standard dose imatinib with interferon alpha (n=84) and low-dose cytarabine (n=11). Median follow-up was 4.8 years (range 1–10). Transcript levels of BCR-ABL, ABL, and GUS were determined by quantitative RT-PCR from samples taken before imatinib onset (“at diagnosis”) and 3 month samples. Only patients expressing typical BCR-ABL transcripts (b2a2 and/or b3a2) were considered. Disease progression was defined by the incidence of accelerated phase, blastic phase or death from any reason. A landmark analysis was performed for progression free survival (PFS) and overall survival (OS) after dichotomizing patients by a cut-off optimized by the cumulative martingale residuals method. Results: The median BCR-ABL/GUS ratio was 15.5% at diagnosis (0.07–271) and 0.62% at 3 months (0–34.7) reflecting a decline by 1.4 log. Disease progression was observed in 17 patients (6.0%), 14 of them died (5.0%). With regard to the above described parameters the following findings were observed: 1) at diagnosis no cut-off level could be identified for BCR-ABL/GUS ratios to separate two prognostic groups according to long-term PFS or OS. 2) At 3 months an optimized 2.8% BCR-ABL/GUS cut-off separated a high-risk group of 61 pts (22% of pts, 8-year PFS 78%, 8-year OS 81%) from a good-risk group of 220 pts (78% of pts, 8-year PFS 94%, 8-year OS 94%, p 〈 0.001, respectively). 3) At 3 months an individual reduction of BCR-ABL transcripts to at least 40% (0.4 log) of the initial level separated best and divided a high-risk group of 33 pts (12% of pts, 8-year PFS 74%, 8-year OS 80%) from a good-risk group of 248 pts (88% of pts, 8-year PFS 93%, 8-year OS 93%, p 〈 0.001, respectively). 4) When the established 10% BCR-ABLIS at 3 months was investigated, 63 pts were high-risk (22% of pts, 8-year PFS 82%, 8-year OS 85%) and 218 good-risk (78% of pts, 8-year PFS 91%, 8-year OS 93%, p=0.002 for PFS, p=0.011 for OS). Conclusions: Initial BCR-ABL transcript levels at diagnosis did not show prognostic significance. To predict survival at 3 months of treatment the absolute transcript level normalized by ABL or GUS can be used. Disclosures: Schnittger: MLL Munich Leukemia Laboratory: Equity Ownership. Hochhaus:Novartis, BMS, MSD, Ariad, Pfizer: Consultancy Other, Honoraria, Research Funding. Müller:Novartis, BMS: Consultancy, Honoraria, Research Funding.

Abstract: Early assessment of BCR-ABL transcript levels at 3 months allows the prediction of survival and may serve as a trigger for treatment intensification in CML patients with slow response to imatinib. The exact decline of BCR-ABL transcript levels within the first 3 months of treatment is defined by the ratio BCR-ABL transcripts at 3 months to BCR-ABL transcripts at baseline. This ratio might better reflect the individual biology of disease and its susceptibility to tyrosine kinase inhibition. Methods A total of 408 chronic phase CML patients (pts) with baseline and 3 month blood samples available in one single laboratory were investigated. Pts with pre-treatment before first blood sampling were excluded (imatinib with or without hydroxyurea, n=58; hydroxyurea only, n=49). A total of 301 evaluable pts (median age 52 years, range 18-85, 41% female) were treated with an imatinib-based therapy within the CML-Study IV. Median follow-up was 4.8 years. Transcript levels of BCR-ABL, total ABL, and beta-glucuronidase (GUS) were determined by quantitative RT-PCR. Exploratory landmark analyses were performed with regard to overall and progression-free survival (OS, PFS) to evaluate the prognostic significance of (i) BCR-ABL/GUS before treatment, (ii) the individual reduction of transcripts given by (BCR-ABL/GUS at 3 months) / (BCR-ABL/GUS before treatment), and (iii) the 3-month 10% BCR-ABLIS landmark. Results The median BCR-ABL/GUS ratio was 15.5% at diagnosis (0.06-107) and 0.63% at 3 months (0-84) reflecting a decline to the 0.04-fold (1.4 log reduction). i) No prognostic cut-off could be identified for BCR-ABL/GUS before treatment. ii) A reduction to the 0.35-fold of the initial BCR-ABL transcript level at diagnosis (0.46 log reduction) was identified as best cut-off according to a hazard ratio of 5.6 (95%-CI 2.3-13.4, p 〈 0.001 for PFS). Using this cut-off a high-risk group of 48 pts (16% of pts, 5-year PFS and OS: 77% and 83%) was separated from a good-risk group of 253 pts (84% of pts, 5-year PFS and OS: 96% and 98%). iii) As a comparison we investigated the 10% BCR-ABLIS landmark at 3 months with a hazard ratio of 2.4 (95%-CI 1.0-5.8, p=0.06 for PFS). With this landmark a high-risk group of 67 pts (22% of pts, 5-year PFS and OS: 87% and 90%) was separated from a good-risk group of 234 pts (78% of pts, 5-year PFS and OS: 95% and 97%). Conclusion A two-group risk stratification according to the individual reduction of BCR-ABL transcripts to the 0.35-fold of pre-treatment levels yields a superior separation of risk groups with a 5-year difference of 19% for PFS and 15% for OS. This predictive marker might identify patients at risk more precisely than 3-month 10% BCR-ABLIS. Disclosures: Hehlmann: BMS: Consultancy, Research Funding; Novartis: Research Funding. Saussele:Novartis: Honoraria, Research Funding, Travel Other; BMS: Honoraria, Research Funding, Travel, Travel Other; Pfizer: Honoraria. Hochhaus:Novartis: Consultancy, Honoraria, Research Funding, Travel Other; BMS: Consultancy, Honoraria, Research Funding; ARIAD: Consultancy, Honoraria; Pfizer: Consultancy. Müller:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Ariad: Consultancy, Honoraria, Research Funding.