The BCR-ABL1 Transcript Type Does Not Influence the Response and the Outcome of Chronic Myeloid Leukemia Patients Treated Frontline with Nilotinib

Chronic myeloid leukemia (CML) is characterized by the presence of the BCR-ABL1 hybrid gene. Different types of BCR-ABL1 fusion transcripts can be found, but the most frequent are the e13a2 (b2a2) and the e14a2 (b3a2). In the tyrosine kinase inhibitors (TKIs) era, few data about the prognostic significance of the transcript type in early chronic phase (ECP) CML are available. Three larger studies suggested that the e13a2 transcript may have an adverse prognostic impact in ECP CML patients treated with imatinib (IM): Vega-Ruiz et al. (251 patients, ASH 2007) reported inferior molecular responses; Lucas et al. (71 patients, Haematologica 2009) reported lower cytogenetic response rates and lower event-free survival (EFS); the GIMEMA CML WP (493 patients, EHA 2011) reported a slower time to major molecular response (MMR) with inferior EFS and progression-free survival (PFS). To our knowledge this is the first evaluation of the prognostic influence of the BCR-ABL1 transcript type on the responses and the outcome of ECP CML treated frontline with nilotinib (NIL).

The CML Italian Registry of Nilotinib includes 215 patients treated with NIL-based regimens. The patients were enrolled within 2 multicenter phase II studies conducted by the GIMEMA CML WP (ClinicalTrials.gov. NCT00481052 and NCT00769327) or treated at the “S. Orsola-Malpighi” University Hospital (Bologna, Italy), with NIL 300 mg BID or 400 mg BID as initial treatment. All the registered patients were analyzed. Patients expressing rare transcripts and patients with both b2a2 and b3a2 transcripts were excluded: 201 out of 215 patients were evaluable, 81 (40%) with e13a2 transcript and 120 (60%) with e14a2 transcript. Differences between groups were tested using χ2 test, Fisher exact test or t-test, as appropriate. Response monitoring: conventional cytogenetic examination (bone marrow) and QPCR (peripheral blood). Definitions: MMR: BCR-ABL^IS ratio <0.1% (International Scale); failures: according to 2009 ELN recommendations; events: failure or treatment discontinuation for any reason. The time-to-response and the outcome were estimated using the Kaplan-Meier method, and compared by log-rank test.

The baseline characteristics of the 2 groups were comparable (no significant differences in age, Sokal/Hasford/EUTOS score distribution, clonal chromosomal abnormalities in Ph+ cells, NIL dose), except for the percentage of basophils in the peripheral blood, higher in patients with e14a2 transcript (3.4% vs 2.3%, p=0.01). The median observation was 29 months (range 18–47); 92% of the patients had at least 2 year observation. The CCgR and MMR rates at 12 months were comparable in the 2 groups. The time to MMR was longer for patients with e13a2 transcript (6 months vs 3 months, p=0.04), but the overall CCgR rates (93.8 vs 91.7, p=0.79) and the overall MMR rates (85.1 vs 90.0, p=0.38) were not significantly different in patients with e13a2 or e14a2 transcript, respectively. The probability of Overall Survival (OS), Progression-Free Survival (PFS) and Failure-Free Survival (FFS) were comparable: 91.4% vs 95.8% (p=0.61), 90.7% vs 95.0% (p=0.51), and 90.7% vs 88.7% (p=0.40) in patients with e13a2 and e14a2 transcript, respectively.

In our experience, based on 201 early CP CML patients treated frontline with NIL with a minimum follow-up of 18 months, the BCR-ABL transcript type did not show any relevant prognostic impact. The time to MMR was longer in patients with e13a2 transcript, but no response and outcome differences have been observed so far. The number of observed events was low and a longer observation is required.

European LeukemiaNet, COFIN, Bologna University, BolognAIL

Castagnetti:Novartis Pharma: Consultancy, Honoraria, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Speakers Bureau. Gugliotta:Novartis: Consultancy, Honoraria; Bristol-Myers-Squibb: Consultancy, Honoraria. Breccia:Bristol Myers Squibb: Consultancy; Novartis: Consultancy. Cavazzini:Novartis Pharma: Honoraria; Bristol Myers Squibb: Honoraria. Turri:Novartis: Consultancy, Novartis Other; Bristol Myers Squibb: Bristol Myers Squibb, Bristol Myers Squibb Other, Consultancy. Soverini:Novartis: Consultancy; Bristol-Myers Squibb: Consultancy; ARIAD: Consultancy. Saglio:Novartis: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; Pfizer: Consultancy. Martinelli:Novartis: Consultancy, Honoraria, Speakers Bureau; Bristol-Myers-Squibb: Consultancy, Honoraria, Speakers Bureau. Baccarani:ARIAD, Novartis, Bristol Myers-Squibb, and Pfizer: Consultancy, Honoraria, Speakers Bureau. Rosti:Novartis Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Speakers Bureau; Pfizer: Speakers Bureau.