Assessment of droplet digital polymerase chain reaction for measuring BCR-ABL1 in chronic myeloid leukaemia in an international interlaboratory study.

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.

Comparison of BCR-ABL1 quantification in peripheral blood and bone marrow using an International Scale-standardized assay for assessment of deep molecular response in chronic myeloid leukemia.

Background Monitoring of molecular response (MR) using quantitative polymerase chain reaction (PCR) for BCR-ABL1 is a pivotal tool for guiding tyrosine kinase inhibitor therapy and the long-term follow-up of patients with chronic myeloid leukemia (CML). Results of MR monitoring are standardized according to the International Scale (IS), and specific time-dependent molecular milestones for definition of optimal response and treatment failure have been included in treatment recommendations. The common practice to use peripheral blood (PB) instead of bone marrow (BM) aspirate to monitor the MR monitoring in CML has been questioned. Some studies described differences between BCR-ABL1 levels in paired PB and BM specimens. Methods We examined 631 paired PB and BM samples from 283 CML patients in a retrospective single-center study using an IS normalized quantitative reverse transcription (qRT)-PCR assay for quantification of BCR-ABL1IS. Results A good overall concordance of BCR-ABL1IS results was found, a systematic tendency towards higher BCR-ABL1IS levels in PB was observed in samples of CML patients in a major MR. This difference was most pronounced in patients treated with imatinib for at least 1 year. Importantly, the difference resulted in a significantly lower rate of deep MR when BCR-ABL1IS was assessed in the PB compared to BM aspirates. Conclusions In summary, our data suggest that the classification of deep MR in patients with CML is more stringent in PB than in BM. Our study supports the current practice to primarily use PB for long-term molecular follow-up monitoring in CML.