Deep Molecular Response in Patients With Newly Diagnosed Chronic Myeloid Leukemia in Chronic Phase (CML-CP) Treated With Nilotinib: ENESTnext Update

Background: The BCR-ABL tyrosine kinase inhibitor nilotinib elicits faster and deeper molecular responses (MRs) vs imatinib in patients with CML-CP. Achievement of sustained deep MR is associated with improved long-term outcomes and is a key criterion for entry into treatment-free remission (TFR) studies. Given the importance of accurately measuring deep MR in patients with CML, increasingly sensitive techniques are needed for monitoring minimal residual disease. In ENESTnext, MR to nilotinib was assessed using conventional methodology (real-time quantitative reverse transcriptase polymerase chain reaction [RQ-PCR]) and a novel microfluidic digital PCR assay that is > 1 log more sensitive than standard RQ-PCR.

Methods: In this single-arm, open-label, multicenter study (NCT01227577), adults with CML-CP diagnosed within 6 months of enrollment were treated with nilotinib 300 mg twice daily (BID) for up to 2 years. Dose escalation to nilotinib 400 mg BID for patients with suboptimal response or treatment failure (per modified European LeukemiaNet 2009 recommendations) was permitted per physician discretion. RQ-PCR evaluation of peripheral blood samples was performed by a central laboratory (monthly for the first 3 months and every 3 months thereafter) according to the International Scale (IS). The primary endpoint is the rate of confirmed (≥ 2 samples taken 3 months apart) MR^4.5 (≥ 4.5-log reduction of BCR-ABL transcript levels; BCR-ABL^IS ≤ 0.0032%) with 2 years of nilotinib therapy; complete cytogenetic response (CCyR) and major MR (MMR; 3-log reduction of BCR-ABL transcript levels; BCR-ABL^IS ≤ 0.1%) were evaluated as secondary endpoints. Per protocol, assessment of cytogenetic response was not required at specified time points for all patients on study. In an exploratory analysis, samples from patients with confirmed MR^4.5by conventional RQ-PCR were also evaluated using the more sensitive Fluidigm digital PCR platform. The data cutoff date for this analysis was April 30, 2014.

Results: A total of 128 patients were enrolled (median age, 56.5 years [range, 21.0-89.0 years]); 64 patients (50.0%) were male and 103 (80.5%) were Caucasian. As of the data cutoff, 45 patients (35.2%) had completed the study, 49 (38.3%) remained on treatment, and 34 (26.6%) had discontinued early. With a median treatment duration of 12.7 months, 88 (68.8%), 94 (73.4%), and 32 (25.0%) patients achieved CCyR, MMR, and MR^4.5, respectively, at any time (Table). Of 32 patients who achieved MR^4.5, 14 achieved MR^4.5 by 6 months. A total of 169 samples from 32 patients with confirmed MR^4.5 by conventional RQ-PCR were analyzed by digital PCR. Using the digital PCR platform, 6 of these patients initially had detectable BCR-ABL transcripts that subsequently became undetectable with continued nilotinib therapy. Of the remaining 26 patients, 12 had BCR-ABL transcripts that were initially undetectable and remained undetectable by digital PCR, 12 had detectable BCR-ABL transcripts that remained detectable, and 2 had undetectable BCR-ABL transcripts that became detectable. The most common (≥ 4 patients) grade 3/4 adverse events (AEs) regardless of relationship to study drug were increased lipase (n = 14), thrombocytopenia (n = 11), neutropenia (n = 8), hypophosphatemia (n = 5), anemia (n = 4), and nausea (n = 4). Reasons for study discontinuation were AEs (n = 15), unsatisfactory therapeutic effect (n = 5), withdrawn consent (n = 4), death (n = 3; causes of death were other malignancy, pneumonia, and not specified/no AE [n = 1 each]), protocol deviation (n = 3), abnormal laboratory values (n = 2), loss to follow-up (n = 1), and administrative problems (n = 1).

Conclusions: Frontline treatment with nilotinib 300 mg BID in patients with newly diagnosed CML-CP led to rapid achievement of MR^4.5 as assessed with conventional RQ-PCR. As > 40% of samples with at least MR^4.5according to standard RQ-PCR were positive using the digital PCR assay, this tool may have potential in evaluating MR to determine eligibility for TFR studies.

^a Cytogenetic response was not assessed in all patients at all time points.