From the laboratory perspective, effective management of patients with chronic myeloid leukemia (CML) requires accurate diagnosis, assessment of prognostic markers, sequential assessment of levels of residual disease and investigation of possible reasons for resistance, relapse or progression. Our scientific and clinical knowledge underpinning these requirements continues to evolve, as do laboratory methods and technologies. The European LeukemiaNet convened an expert panel to critically consider the current status of genetic laboratory approaches to help diagnose and manage CML patients. Our recommendations focus on current best practice and highlight the strengths and pitfalls of commonly used laboratory tests.

• MeSH
• Leukemia, Myelogenous, Chronic, BCR-ABL Positive * diagnosis   genetics   therapy   MeSH
• Protein Kinase Inhibitors * MeSH
• Humans MeSH
• Recurrence MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Protein Kinase Inhibitors * MeSH

Standardized monitoring of BCR::ABL1 mRNA levels is essential for the management of chronic myeloid leukemia (CML) patients. From 2016 to 2021 the European Treatment and Outcome Study for CML (EUTOS) explored the use of secondary, lyophilized cell-based BCR::ABL1 reference panels traceable to the World Health Organization primary reference material to standardize and validate local laboratory tests. Panels were used to assign and validate conversion factors (CFs) to the International Scale and assess the ability of laboratories to assess deep molecular response (DMR). The study also explored aspects of internal quality control. The percentage of EUTOS reference laboratories (n = 50) with CFs validated as optimal or satisfactory increased from 67.5% to 97.6% and 36.4% to 91.7% for ABL1 and GUSB, respectively, during the study period and 98% of laboratories were able to detect MR4.5 in most samples. Laboratories with unvalidated CFs had a higher coefficient of variation for BCR::ABL1IS and some laboratories had a limit of blank greater than zero which could affect the accurate reporting of DMR. Our study indicates that secondary reference panels can be used effectively to obtain and validate CFs in a manner equivalent to sample exchange and can also be used to monitor additional aspects of quality assurance.

• MeSH
• Fusion Proteins, bcr-abl genetics   MeSH
• Leukemia, Myelogenous, Chronic, BCR-ABL Positive * diagnosis   genetics   MeSH
• Humans MeSH
• Reference Standards MeSH
• Treatment Outcome MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Fusion Proteins, bcr-abl MeSH

BCR-ABL1 molecular detection using quantitative PCR (qPCR) methods is the golden standard of chronic myeloid leukemia (CML) monitoring. However, due to variable sensitivity of qPCR assays across laboratories, alternative methods are tested. Digital PCR (dPCR) has been suggested as a robust and reproducible option. Here we present a comparison of droplet dPCR with routinely used reverse-transcription qPCR (RT-qPCR) and automated GeneXpert systems. Detection limit of dPCR was above 3 BCR-ABL1 copies, although due to background amplification the resulting sensitivity was 0.01% BCR-ABL1 (MR4.0). Nevertheless, in comparison with GeneXpert, dPCR categorized more than 50% of the patients into different MR groups, showing a potential for improved BCR-ABL1 detection.

• Keywords
• BCR-ABL1 monitoring, CML, chronic myeloid leukemia, Chronic myeloid leukemia, Digital PCR, EAC, Europe Against Cancer, FPR, false positivity rate, GeneXpert BCR-ABL Monitor assay, IS, international scale, LOB, limit of blank, LOD, limit of detection, MR, molecular response, NTC, no template control, RT-qPCR, RT-qPCR, reverse-transcription quantitative PCR, TKI, tyrosine kinase inhibitors, cDNA, complementary DNA, dPCR, digital PCR, pDNA, plasmid DNA, qPCR, quantitative PCR,
• Publication type
• Journal Article MeSH

PURPOSE: The advent of tyrosine kinase inhibitor (TKI) therapies has revolutionized the treatment of chronic myeloid leukemia (CML). The European LeukemiaNet (ELN) recommends quantification of BCR-ABL1 transcripts by real-time quantitative PCR every 3 months during TKI treatment. Since a proportion of patients in deep molecular response (DMR: MR4, MR4.5, MR5) maintain remission after treatment stop, assessment of DMR is crucial. However, systematically collected molecular data, monitored with sensitive standardized assays, are not available outside clinical trials. METHODS: Data were collected on the standardized assessment of molecular response in the context of real-life practice. BCR-ABL1 transcript levels after > 2 years of TKI therapy were evaluated for DMR by local laboratories as well as standardized EUTOS laboratories. Since standardized molecular monitoring is a prerequisite for treatment discontinuation, central surveillance of the performance of the participating laboratories was carried out. RESULTS: Between 2014 and 2017, 3377 peripheral blood samples from 1117 CML patients were shipped to 11 standardized reference laboratories in six European countries. BCR-ABL1 transcript types were b3a2 (41.63%), b2a2 (29.99%), b2a2/b3a2 (3.58%) and atypical (0.54%). For 23.72% of the patients, the initial transcript type had not been reported. Response levels (EUTOS laboratory) were: no MMR, n = 197 (6.51%); MMR, n = 496 (16.40%); MR4, n = 685 (22.64%); MR4.5, n = 937 (30.98%); MR5, n = 710 (23.47%). With a Cohen's kappa coefficient of 0.708, a substantial agreement between EUTOS-certified and local laboratories was shown. CONCLUSIONS: Multicenter DMR assessment is feasible in the context of real-life clinical practice in Europe. Information on the BCR-ABL1 transcript type at diagnosis is crucial to accurately monitor patients' molecular response during or after TKI therapy.

• Keywords
• BCR–ABL, CML, Chronic myeloid leukemia, Deep molecular remission, Eureka, Molecular monitoring, Standardization, TFR, Treatment-free remission,
• MeSH
• Leukemia, Myeloid, Chronic-Phase blood   drug therapy   genetics   MeSH
• Leukemia, Myelogenous, Chronic, BCR-ABL Positive blood   drug therapy   genetics   MeSH
• Adult MeSH
• Protein Kinase Inhibitors administration & dosage   MeSH
• Cohort Studies MeSH
• Laboratories standards   statistics & numerical data   MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Registries MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Europe MeSH
• Names of Substances
• Protein Kinase Inhibitors MeSH