Achievement Of a MR^5.0 Within the Randomized CML-Study IV: Feasibility, Differences Between Treatment Arms, and Prognostic Implications

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 MR^5.0 in pts on imatinib (IM)-based treatment.

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 MR^5.0 the BCR-ABL^IS 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.

In 1,198 of the 1,442 molecularly examined pts at least one sample fulfilled the sensitivity criteria for a MR^5.0 (8,266 of 24,101 samples, 34.3%). Cumulative incidence of MR^5.0 was 51% at 8 years. The median time to MR^5.0 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 MR^5.0 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 MR^5.0. Taken all treatment arms together, our analyses have shown that the chance of achieving a MR^5.0 by 8 years was considerably reduced if the pts had a BCR-ABL^IS >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%).

This evaluation of a large randomized trial reveals feasibility of MR^5.0 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 MR^5.0. 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.

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.