Molecular Response After 3 Months of 1st Line Imatinib Therapy Is Predictive for Treatment Failure and Disease Progression In Patients with Chronic Phase Chronic Myeloid Leukemia - a Follow-up Analysis of the German CML Study IV

The lack of a sufficient response to first line imatinib treatment has been observed in a substantial proportion of CML patients and has been associated with an inferior survival. Therefore, response criteria have been defined to identify patients with treatment failure. A change of drug therapy to 2^nd generation tyrosine kinase inhibitors or allogeneic stem cell transplantation is recommended for this group of patients (European LeukemiaNet, ELN, Baccarani et al., JCO 2009). We sought to evaluate the predictive value of early molecular response landmarks for treatment failure and disease progression to identify patients at risk and to provide a guidance for the interpretation of BCR-ABL levels.

949 patients included into the randomized German CML Study IV and treated with an imatinib based therapy consisting of standard dose imatinib (400 mg/d), high dose imatinib (800 mg/d) and combinations of standard dose imatinib with low dose cytarabine or interferon alpha were evaluable for molecular and cytogenetic analysis. BCR-ABL (IS) was determined by quantitative RT-PCR. The type of BCR-ABL transcript (b2a2, n=424; b3a2, n=464; b2a2 and b3a2, n=148) was defined by multiplex PCR. Patients with atypical BCR-ABL transcripts were excluded from the analysis. Cytogenetic response (CyR) was determined by G-banding metaphase analyses. Treatment failure has been defined according to ELN criteria as a lack of major CyR after 12 months and a lack of complete CyR after 18 months of imatinib treatment, respectively. CyR data were available for 479 pts between 12 and 18 months with a subset of 289 pts evaluable for 3 month molecular response (CyR data after 18 months, n=532; 3 month molecular subset, n=289). Disease progression comprises the incidence of accelerated phase, blast phase and death. Median follow-up for disease progression was 35 months (range 2–85). Fisher's exact test has been performed to evaluate the prognostic significance of 3 month BCR-ABL landmarks for 12 month and 18 month treatment failure. A landmark analysis has been performed for disease progression (logrank test).

In 20 of 289 evaluable pts treatment failure has been observed after 12 months, and in 29 of 289 pts after 18 months. 24 of 570 evaluable pts showed a disease progression after a median of 18 months (range 5–71). A stratification into three groups at 3 months reveals a significant difference concerning treatment failure between pts with BCR-ABL levels between 1% and 10% and those with BCR-ABL levels >10%. With regard to disease progression there is a statistical trend. Comparing two groups the 10% BCR-ABL cut-off is highly significant for both, treatment failure and disease progression. Missing the 10% BCR-ABL landmark after 3 months of imatinib treatment defines a poor risk group with a 20.7% risk of treatment failure after 18 months and a 8.1% risk of disease progression (Table).

Early assessment of molecular response after 3 months of imatinib therapy allows the identification of a patient cohort with an increased risk of treatment failure and disease progression.

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Müller:Novartis Corporation: Honoraria, Research Funding. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Hochhaus:Novartis Corporation: Honoraria, Research Funding.