Nilotinib 300 mg BID as frontline treatment of CML: Prospective analysis of the Xpert BCR-ABL Monitor system and significance of 3-month molecular response

Monitoring of Minimal Residual Disease (MRD) in Chronic Myeloid Leukemia: Recent Advances

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by the BCR-ABL1 fusion gene generation as a consequence of the t(9;22)(q34;q11) rearrangement. The identification of the BCR-ABL1 transcript was of critical importance for both CML diagnosis and minimal residual disease (MRD) monitoring. In this review, we report the recent advances in the CML MRD monitoring based on RNA, DNA and protein analysis. The detection of the BCR-ABL1 transcript by the quantitative reverse-transcriptase polymerase chain reaction is the gold standard method, but other systems based on digital PCR or on GeneXpert technology have been developed. In the last years, DNA-based assays showed high sensitivity and specificity, and flow cytometric approaches for the detection of the BCR-ABL1 fusion protein have also been tested. Recently, new MRD monitoring systems based on the detection of molecular markers other than the BCR-ABL1 fusion were proposed. These approaches, such as the identification of CD26+ leukemic stem cells, microRNAs and mitochondrial DNA mutations, just remain preliminary and need to be implemented. In the precision medicine era, the constant improvement of the CML MRD monitoring practice could allow clinicians to choose the best therapeutic algorithm and a more accurate selection of CML patients eligible for the tyrosine kinase inhibitors discontinuation.

Patient-Initiated Discontinuation of Tyrosine Kinase Inhibitor for Chronic Myeloid Leukemia

The introduction of tyrosine kinase inhibitors (TKI) has revolutionised the management of patients with chronic myeloid leukemia (CML) over the last twenty years, but despite significant improvements in survival, patients exhibit long-term side effects that impact on quality of life. A major advance in CML management has been the ability to discontinue TKI therapy achieving a treatment-free remission (TFR), yet this option is only available to eligible patients who present with low-risk disease and who subsequently attain deep and sustained molecular responses. A case is described of a patient with CML who self-initiated stopping of TKI therapy when in a less than optimal molecular remission. Despite this action, the patient continues to experience a TFR with prospective close molecular monitoring performed. It is emphasized that this approach may lead to ineffective treatment discontinuation, molecular relapse, and increased patient anxiety. As TFR for patients with CML moves from clinical trials into routine clinical practice, emphasis is placed on adherence to (evolving) guidelines critical to ensure optimal counselling, selection, monitoring, and continued management of patients whether TFR is successful or not.

Nilotinib treatment induced large granular lymphocyte expansion and maintenance of longitudinal remission in a Philadelphia chromosome-positive acute lymphoblastic leukemia

It is well known that the second-generation tyrosine kinase inhibitor dasatinib evokes an immunological reaction as an off-target effect and induces large granular lymphocytes (LGLs) expansion in 30% of patients. However, LGLs expansion in nilotinib-treated patients is rare. We report the case of a 65-year-old patient with Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL) who showed LGLs expansion during nilotinib treatment. The patient achieved complete remission (CR) after multi-agent chemotherapy combined with dasatinib treatment. However, ALL relapsed in the central nervous system and bone marrow when treatment was interrupted due to interstitial pneumonia. Nilotinib treatment was subsequently started and the patient achieved second CR. Marked peripheral blood lymphocytosis emerged after the start of nilotinib treatment. CD8 + CD57 + cytotoxic T cells were predominantly expanded and showed strong cytocidal activity against K562 Ph-positive leukemia cells. These results suggest that similar to dasatinib, nilotinib can induce LGLs expansion, possibly contributing to long-term remission in patients with Ph-ALL.

Rates of deep molecular response by digital and conventional PCR with frontline nilotinib in newly diagnosed chronic myeloid leukemia: a landmark analysis

ENESTnext (NCT01227577) was a single-arm, multicenter trial evaluating the rate of deep molecular response by 2 years in patients with newly diagnosed (within 6 months) chronic myeloid leukemia in chronic phase (CML-CP) treated with nilotinib 300 mg twice daily. Among 128 enrolled patients, 94 (73%) achieved major molecular response (MMR; BCR-ABL1 ≤ 0.1% on the International Scale [BCR-ABL1IS]) and 34 (27%) achieved confirmed MR4.5 (BCR-ABL1IS ≤0.0032% detectable or undetectable; primary endpoint) by 2 years. Three-month BCR-ABL1 levels were predictive of later responses. In exploratory analyses, digital polymerase chain reaction (PCR) detected BCR-ABL1 in 39.4% of samples from patients with confirmed MR4.5 and identified further decreases in BCR-ABL1 with continued nilotinib. Safety results, including cardiovascular events, were consistent with those in other nilotinib trials. These results further substantiate the molecular response rates associated with frontline nilotinib therapy and demonstrate the feasibility of monitoring very low BCR-ABL1 transcript levels using digital PCR.

Feasibility of Qualitative Testing of BCR-ABL and JAK2 V617F in Suspected Myeloproliperative Neoplasm (MPN) Using RT-PCR Reversed Dot Blot Hybridization (RT-PCR RDB)

BACKGROUND

Defining the presence of BCR-ABL transcript in suspected myeloproliferative neoplasm is essential in establishing chronic myeloid leukemia. In the absence of BCR-ABL, the conventional diagnostic algorithm recommends JAK2 V617F mutation testing to support diagnosis of other MPN diseases such as polycythemia vera, essential thrombocythemia, and primary myelofibrosis. In certain cases of thrombocythemia, simultaneous upfront testing of both BCR-ABL and JAK2 may be desirable. We wanted to test the feasibility of multiplex detection of BCR-ABL transcript variants and JAK2 V617F mutation simultaneously using the reverse transcriptase polymerase chain reaction (RT-PCR)-based reverse dot-blot hybridization (RDB) method.

MATERIAL AND METHODS

Separate biotinylated RT-PCR primers were designed to amplify specific BCR-ABL transcripts and JAK2 V617F mutant alleles. Specific hybridization of RT-PCR products with arrays of membrane-bound probes followed by colorimetric development would allow simultaneous visualization of BCR-ABL and/or JAK2 mutant transcripts in a given specimen. To validate the RDB method, we used cDNA specimens previously referred to our laboratory for routine clinical testing of BCR-ABL and/or JAK2.

RESULTS

The limit of detection or analytical sensitivity of the RDB method using cDNA specimens was 0.5% and 6.25% in detecting BCR-ABL and JAK2 mutant transcripts, respectively. The diagnostic specificity and sensitivity to detect BCR-ABL and JAK2 were 100% and 92.3% (N = 38); and 100% and 100% (N = 27), respectively. RDB also detected BCR-ABL transcripts in 22% of JAK2 V617F mutation-positive samples (N = 14).

CONCLUSIONS

RT-PCR RDB is a promising qualitative multiplex method to detect BCR-ABL and JAK2 mutant transcripts simultaneously.

A BCR-ABL1 cutoff of 1.5% at 3 months, determined by the GeneXpert system, predicts an optimal response in patients with chronic myeloid leukemia

In chronic myeloid leukemia (CML) patients, 3-month BCR-ABL1 levels have consistently been correlated with further outcomes. Monitoring molecular responses in CML using the GeneXpert (Cepheid) platform has shown an optimal correlation with standardized RQ-PCR (IS) when measuring BCR-ABL1 levels lower than 10%, as it is not accurate for values over 10%. The aim of the present study was to determine the predictive molecular value at three months on different outcome variables using the Xpert BCR-ABL1 Monitor^TM assay (Xpert BCR-ABL1). We monitored 125 newly diagnosed consecutive CML patients in the chronic phase (CML-CP) using an automated method: Xpert BCR-ABL1. Only 5% of patients did not achieve an optimal response at 3 months, and the 10% BCR-ABL1 cutoff defined by RQ-PCR (IS) methods was unable to identify significant differences in the probabilities of achieving a complete cytogenetic response (CCyR) (50% vs. 87%, p = 0.1) or a major molecular response (MMR) (60% vs. 80%, p = 0.29) by 12 months. In contrast, a cutoff of 1.5% more accurately identified differences in the probabilities of achieving CCyR (98% vs. 54%, p<0.001) and MMR (88% vs. 56%, p<0.001) by 12 months, as well as probabilities of treatment changes (p = 0.005). Therefore, when using the Xpert BCR-ABL1 assay, a cutoff of 1.5% at 3 months could with high probability identify patients able to achieve an optimal response at 12 months.

Current developments in molecular monitoring in chronic myeloid leukemia

Molecular monitoring plays an essential role in the clinical management of chronic myeloid leukemia (CML) patients, and now guides clinical decision making. Quantitative reverse-transcriptase-polymerase-chain-reaction (qRT-PCR) assessment of BCR-ABL1 transcript levels has become the standard of care protocol in CML. However, further developments are required to assess leukemic burden more efficiently, monitor minimal residual disease (MRD), detect mutations that drive resistance to tyrosine kinase inhibitor (TKI) therapy and identify predictors of response to TKI therapy. Cartridge-based BCR-ABL1 quantitation, digital PCR and next generation sequencing are examples of technologies which are currently being explored, evaluated and translated into the clinic. Here we review the emerging molecular methods/technologies currently being developed to advance molecular monitoring in CML.

A longitudinal evaluation of performance of automated BCR-ABL1 quantitation using cartridge-based detection system

SummaryAn automated cartridge-based detection system (GeneXpert; Cepheid) is being widely adopted in low throughput laboratories for monitoring BCR-ABL1 transcript in chronic myelogenous leukaemia. This Australian study evaluated the longitudinal performance specific characteristics of the automated system.

The automated cartridge-based system was compared prospectively with the manual qRT-PCR-based reference method at SA Pathology, Adelaide, over a period of 2.5 years. A conversion factor determination was followed by four re-validations. Peripheral blood samples (n = 129) with international scale (IS) values within detectable range were selected for assessment. The mean bias, proportion of results within specified fold difference (2-, 3- and 5-fold), the concordance rate of major molecular remission (MMR) and concordance across a range of IS values on paired samples were evaluated.

The initial conversion factor for the automated system was determined as 0.43. Except for the second re-validation, where a negative bias of 1.9-fold was detected, all other biases fell within desirable limits. A cartridge-specific conversion factor and efficiency value was introduced and the conversion factor was confirmed to be stable in subsequent re-validation cycles. Concordance with the reference method/laboratory at >0.1–≤10 IS was 78.2% and at ≤0.001 was 80%, compared to 86.8% in the >0.01–≤0.1 IS range. The overall and MMR concordance were 85.7% and 94% respectively, for samples that fell within ± 5-fold of the reference laboratory value over the entire period of study.

Conversion factor and performance specific characteristics for the automated system were longitudinally stable in the clinically relevant range, following introduction by the manufacturer of lot specific efficiency values.

Prognostic significance of early molecular response in chronic myeloid leukemia patients treated with tyrosine kinase inhibitors

A 55-year-old man presented with splenomegaly (10 cm below left costal margin) and leucocytosis (145 × 10(9)/L). Differential showed neutrophilia with increased basophils (2%), eosinophils (1.5%), and left shift including myeloblasts (3%). A diagnosis of chronic myeloid leukemia in chronic phase was established after marrow cytogenetics demonstrated the Philadelphia chromosome. Molecular studies showed a BCR-ABL1 qPCR result of 65% on the International Scale. Imatinib therapy at 400 mg daily was initiated due to patient preference, with achievement of complete hematological response after 4 weeks of therapy. BCR-ABL1 at 1 and 3 months after starting therapy was 37% and 13%, respectively (all reported on International Scale). Is this considered an adequate molecular response?