ALBERT

Description: Molecular analysis is recommended for monitoring patients (pts) with CML. For imatinib treated pts in chronic phase (CP), molecular analysis provides important prognostic information. A major molecular response (MMR, BCR-ABL ≤0.1% IS (international scale)) is associated with favourable progression free survival and is a primary endpoint of clinical trials. The 3 month (m) BCR-ABL level is predictive of MMR and almost all de-novo pts with values ≤1.0% IS subsequently achieve MMR. The second generation tyrosine kinase inhibitors nilotinib and dasatinib (2TKI) have demonstrated efficacy for CP pts who fail imatinib therapy due to resistance or intolerance. However, treatment failure associated with the presence of a limited spectrum of resistant mutations is evident. Furthermore, it has recently been suggested that failure to achieve a major cytogenetic response (MCR) by 12m defines inadequate response and these pts should be considered for alternative therapies (Cortes et al, Blood,2008,112,516). Pts in minor cytogenetic response or complete hematologic response at 12m had a projected 1 year progression rate of 17% compared to 3% for those with MCR at 12m. The value of molecular monitoring in the setting of 2TKI has not been defined in terms of the early prediction of response or emergence of resistant mutations. We monitored BCR-ABL levels and mutation status in 155 CP pts treated with nilotinib (n=73; 400mg BD) or dasatinib (n=82; ≥100mg (76/82 70mg BD)) after imatinib failure for a median of 18m (range (r) 3–36). The BCR-ABL level at 3m of 2TKI was highly predictive of subsequent MMR, P10% IS rather than upon a significant rise. The rise associated with emergent mutations when BCR-ABL was ≤10% IS was significantly higher: median 7.3-fold, P10% IS are at risk of acquiring 2TKI resistant mutations and would benefit from regular mutation screening until BCR-ABL falls below 10% IS. Thereafter, a significant rise of 〉5-fold in BCR-ABL should trigger mutation screening. Figure Figure

Description: Treatment of chronic myeloid leukemia (CML) with the tyrosine kinase inhibitors (TKIs) imatinib mesylate and nilotinib represents a successful application of molecularly targeted anticancer therapy. However, the effect of TKIs on leukemic stem cells remains incompletely understood. On the basis of a statistical modeling approach that used the 10-year imatinib mesylate treatment response of patients with CML and a patient cohort receiving first-line nilotinib therapy, we found that successful long-term therapy results in a triphasic exponential decline of BCR-ABL1 transcripts in many patients. Within our framework, the first slope of −0.052 ± 0.018 (imatinib mesylate) and −0.042 ± 0.015 (nilotinib) per day represents the turnover rate of leukemic differentiated cells, whereas the second slope of −0.0057 ± 0.0038 (imatinib mesylate) and −0.0019 ± 0.0013 (nilotinib) per day represents the turnover rate of leukemic progenitor cells. The third slope allows an inference of the behavior of immature leukemic cells, potentially stem cells. This third slope is negative in most patients, positive in others, and not observable in some patients. This variability in response may be because of insufficient follow-up, missing data, disease heterogeneity, inconsistent compliance to drug, or acquired resistance. Our approach suggests that long-term TKI therapy may reduce the abundance of leukemic stem cells in some patients.

Description: Key Points The association between multiple BCR-ABL1 mutations and inferior response to nilotinib/dasatinib was not seen with ponatinib therapy. However, chronic phase patients with T315I plus additional mutation(s) did have poorer responses to ponatinib than those with T315I only.

Description: Abstract 165 Introduction. The opportunity to discontinue kinase inhibitor therapy while maintaining a deep remission is desirable for many CML patients. Despite good responses to imatinib for most patients, treatment related side effects remain problematic and can affect quality of life. Studies have demonstrated that a proportion of carefully selected patients can sustain response after imatinib discontinuation. The first requirement for successful discontinuation is likely to be stable deep molecular response based on a sensitive RQ-PCR assay. The criteria for patient selection in the French Stop Imatinib (STIM) and Australian CML8 (TWISTER) imatinib discontinuation trials included stable undetectable BCR-ABL1 transcripts for at least 24 months with a PCR sensitivity of 5 and 4.5 log, respectively. The probability of continued remission after discontinuation for imatinib treated patients without prior interferon-α therapy was approximately 33%. It is not known how many imatinib treated patients will eventually meet these PCR criteria for a discontinuation trial. Aims. We aimed to determine 1) the cumulative probability of achieving the PCR criteria for imatinib discontinuation as defined in the CML8 study, and 2) factors that predicted its achievement. Method. The molecular response of 415 de-novo CML patients in chronic phase enrolled in consecutive clinical trials of imatinib since July 2000 was examined. The assigned daily imatinib dose was 400 mg for 90 patients, 600 mg for 202 patients and 800 mg for 123 patients. Molecular data were included until imatinib cessation or last follow-up. The minimum time since commencing imatinib was 30 months and the median time on imatinib was 45 months, range 3 to 136. The CML8 PCR criteria for imatinib discontinuation were confirmed undetectable BCR-ABL1 transcripts at a sensitivity of 4.5 log that remained undetectable on all PCR tests for at least 24 months while on imatinib therapy. In the current analysis the CML8 PCR discontinuation criteria are defined as ‘stable UMR4.5'. Results. At 8 years of imatinib therapy the cumulative incidence of stable UMR4.5 was 43%, Figure A. Patients were divided into groups according to the time to a confirmed major molecular response (MMR): by 3, 6, 12 or 18 months. There was a significant difference in stable UMR4.5, P

Description: Key PointsIndependent predictors of stable, undetectable BCR-ABL1 during first-line imatinib therapy were female sex and the BCR-ABL1 value at 3 months. Time to achieve an MMR influenced time to stable, undetectable BCR-ABL1, suggesting slower dynamics of BCR-ABL1 decline with delayed MMR.

Description: Background BCR-ABL1 mutations (muts) frequently cause resistance to tyrosine kinase inhibitors (TKIs) in CML. T315I, the most common mut, confers resistance to 1st and 2nd generation TKIs. In vitro studies suggest that all common individual muts are sensitive to the pan-BCR-ABL1 TKI ponatinib, and durable responses have been observed in patients (pts) with T315I. We have shown that low level muts below the detection limit of Sanger sequencing (SS) are important clinically, and that pts with 〉1 mut are a poor risk subgroup with lower CCyR and MMR rates and higher risk of treatment failure on 2nd-line therapy with nilotinib or dasatinib (Parker Blood 2012). Aim To determine whether the presence of low level BCR-ABL1 muts detected by mass spectrometry (mass spec) adversely impacts response to ponatinib. Methods We assessed 376 of the 392 pts treated with ponatinib in the phase II PACE trial who consented for sensitive mass spec mut analysis (detects 32 muts, limit ∼0.2%; 240 CP, 77 AP, 42 BP, 17 Ph+ ALL). RNA from samples collected at trial Day 1 were received from the commercial lab that performed SS. We performed mass spec analysis on duplicate cDNA samples blinded to the SS results. Muts were considered present if detected in both replicates. Cumulative incidence of MCyR, CCyR and MMR were calculated and tested with Gray's K-sample test. Progression free survival (PFS) was assessed by Kaplan-Meier with the log-rank test. 146 pts had disease progression. Mut analysis was performed by SS at discontinuation for 98 pts at the commercial lab. Pts remaining on study had a minimum follow up of 18 months (mo). Results Of the 376 pts, 373 were evaluable at Day 1 by SS, and 359 by mass spec. Muts (242) were detected in 196 pts (53%) by SS. Among these muts, 95% were included in the mass spec assay and were potentially detectable; mass spec detected all but 6. At Day 1, 〉1 mut was detected in more pts by mass spec (64, up to 8 per pt) than SS (42, up to 3 per patient), 17% v 11%. T315I was the most common mut detected. Using mass spec, we detected an additional 12 pts with T315I compared with SS (107 v 95). Of these pts, 73 had T315I only and 34 had T315I plus at least 1 additional mut by mass spec. By SS, 75 pts had T315I only and 20 had T315I plus another mut. At Day 1, mass spec detected 77 low level muts in 53 pts that were not detected by SS. Mut analysis was performed at discontinuation for 10/53 pts. In contrast to our previous studies where certain low level mutants known to confer resistance rapidly expanded with 2nd generation TKI treatment after imatinib resistance, only 2 of the low level mutants expanded during ponatinib therapy and were detected by SS at discontinuation (2 T315I). This supports the pan-BCR-ABL1 inhibition predicted from pre-clinical studies. To investigate relationships between mass spec mut status and response and PFS, pts were grouped according to presence of 1) T315I only, 2) T315I plus additional mut, 3) 〉1 mut (not T315I), 4) 1 mut (not T315I), 5) no mut. The cumulative incidence of MCyR, CCyR and MMR and probability of PFS for AP, BP and Ph+ ALL pts was not significantly different according to mut status. However, among CP pts, significant differences were seen for response and PFS (Figure). Among the CP pts without T315I, pts with no mut had significantly inferior cytogenetic and molecular responses than pts with 〉1 mut, but PFS was not significantly different. For CP pts with T315I, the presence of additional mut was associated with significantly inferior cytogenetic responses and PFS. At 18mo, the cumulative incidence of MCyR, CCyR and MMR for pts with T315I only was 76%, 74% and 64%, respectively, whereas it was 50%, 44% and 33%, respectively, for pts with T315I plus additional mut. PFS at 18 mo was 88% for pts with T315I only, compared with 59% for pts with T315I plus additional mut. Notably, 56% (10/18) of CP pts with T315I plus additional mut as determined by mass spec were not classed as such by SS. Conclusion Mass spec identified a subgroup of CP pts with the T315I mut who had relatively inferior responses and outcome. These pts had T315I plus additional mut at Day 1 by mass spec. These pts also had inferior PFS as compared to pts without muts. Multiple muts in pts with T315I may be a marker of longer disease duration or poor disease control, but suggests that BCR-ABL1 mut status determined by mass spec has prognostic value. Ponatinib may overcome the poor responses to 2nd generation TKIs observed for pts with 〉1 mut without T315I and for pts with a single T315I mut. Disclosures: Yeung: Novartis: Honoraria, Research Funding; BMS: Honoraria. Lustgarten:ARIAD: employees of and own stock/stock options in ARIAD Pharmaceuticals, Inc Other, Employment. Hodgson:ARIAD: Employment, Equity Ownership. Rivera:ARIAD: Employment, Equity Ownership. Hughes:Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Ariad: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Branford:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Ariad: Honoraria, Research Funding.