Measurement of BCR activator of RhoGEF and GTPase -ABL proto-oncogene 1, non-receptor tyrosine kinase (BCR-ABL1) mRNA levels by reverse transcription quantitative polymerase chain reaction (RTqPCR) has been critical to treatment protocols and clinical trials in chronic myeloid leukaemia; however, interlaboratory variation remains a significant issue. Reverse transcriptase droplet digital PCR (RTddPCR) has shown potential to improve testing but a large-scale interlaboratory study is required to definitively establish this. In the present study, 10 BCR-ABL1-positive samples with levels ranging from molecular response (MR)1·0 -MR5·0 were tested by 23 laboratories using RTddPCR with the QXDX BCR-ABL %IS kit. A subset of participants tested the samples using RTqPCR. All 23 participants using RTddPCR detected BCR-ABL1 in all samples to MR4·0 . Detection rates for deep-response samples were 95·7% at MR4·5 , 78·3% at MR4·7 and 87·0% at MR5·0 . Interlaboratory coefficient of variation was indirectly proportional to BCR-ABL1 level ranging from 29·3% to 69·0%. Linearity ranged from 0·9330 to 1·000 (average 0·9936). When results were compared for the 11 participants who performed both RTddPCR and RTqPCR, RTddPCR showed a similar limit of detection to RTqPCR with reduced interlaboratory variation and better assay linearity. The ability to detect deep responses with RTddPCR, matched with an improved linearity and reduced interlaboratory variation will allow improved patient management, and is of particular importance for future clinical trials focussed on achieving and maintaining treatment-free remission.

Advanced Therapies National Institute for Biological Standards and Control Potters Bar UK

Clinical Research Division Fred Hutchinson Cancer Research Center Seattle WA USA

Department of Clinical and Experimental Medicine University of Pisa Pisa Italy

Department of Genomics Strand Life Sciences Bangalore India

Department of Haematology Inselspital Bern University Hospital Bern Switzerland

Department of Haematology Sheffield Teaching Hospitals NHS Foundation Trust Sheffield UK

Department of Hematology and Blood Transfusion University of Medicine and Pharmacy Vietnam National University Hanoi Vietnam

Department of Laboratory Medicine ASST Grande Ospedale Metropolitano Niguarda Milan Italy

Department of Laboratory Medicine University Hospitals Leuven Leuven Belgium

Department of Laboratory Medicine University Medical Center Groningen University of Groningen Groningen Netherlands

Department of Molecular Genetics Institute of Hematology and Blood Transfusion Praha Czech Republic

Department of Oncology KU Leuven Leuven Belgium

Department of Pathology Division of Haematology Queen Mary Hospital Hong Kong Hong Kong

Department of Pathology The University of Hong Kong Hong Kong Hong Kong

Department of Surgical Pathology Zealand University Hospital Roskilde Denmark

Department of Transfusion Medicine University Hospital Leipzig Leipzig Germany

Digital Biology Group Bio Rad Pleasanton CA USA

Faculty of Medicine Dentistry and Health Department of Oncology and Metabolism University of Sheffield Sheffield UK

Genetics and Molecular Biology National Institute of Hematology and Blood Transfusion Hanoi Vietnam

Haematology Laboratory Hôpital Saint Louis Paris France

Laboratory of Hematology University Hospital Centre Bordeaux Pessac France

Pathology Hong Kong Sanatorium and Hospital Hong Kong Hong Kong

Personalized Medicine Service Tan Tock Seng Hospital Singapore Singapore

Sheffield Diagnostic Genetics Service Sheffield Children's Hospital NHS Foundation Trust Sheffield UK

Sheffield Teaching Hospital NHS Foundation Trust UK National External Quality Assessment Services for Leucocyte Immunophenotyping Sheffield UK

University of Bordeaux INSERM U1218 Bordeaux France

University of Southampton School of Medicine Southampton UK

Wessex Regional Genetics Laboratory Salisbury District Hospital Salisbury UK

West Midlands Regional Genetics Laboratory Birmingham Women's and Children's Hospitals NHS Foundation Trust Birmingham UK

Br J Haematol. 2021 Jul;194(1):11-13. doi: 10.1111/bjh.17520. PubMed

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Impact of BCR::ABL1 transcript type on RT-qPCR amplification performance and molecular response to therapy