Persistent chronic myeloid leukemia (CML) in patients previously thought to be in remission can be detected with digital polymerase chain reaction (dPCR), according to a recent study in The Journal of Molecular Diagnostics.1

CML is characterized by the involvement of the BCR-ABL1 tyrosine kinase protein, and so tyrosine kinase inhibitor (TKI) treatment has drastically improved the prognosis of patients with CML. In spite of this, 60% of the patients who underwent TKI treatment until they had no detectable blood biomarkers of CML had to restart TKI therapy upon the return of detectable CML. CML has been detected through transcripts of the BCR-ABL1 gene by reverse-transcription quantitative PCR, which are analyzed in peripheral blood samples.

This study used dPCR, a DNA-based digital assay that can detect lower levels of BCR-ABL1-positive disease. The assay uses a high-performing DNA-based hydrolysis probe that is specific to the molecular trace of each patient’s CML clone. This use of target-enriched next-generation sequencing uses DNA, which is more stable than the RNA used by reverse-transcription PCR. The authors described it as “relatively simple, cost-effective, and suited to a high-throughput laboratory.”

Continue Reading

This study assessed the sensitivity of dPCR compared with 3 other more commonly used quantitative PCR approaches. The study tested 46 follow-up samples from 6 patients with diagnoses of early CML. Among the 46 samples, 36 were considered to be in deep molecular remission. From these 46 samples, persistent CML was detected by dPCR in 81%, by DNA-based quantitative PCR in 19%, and by real-time digital PCR in 25%. Overall, dPCR was far more sensitive in detecting persistent CML than 2 other more commonly used quantitative PCR techniques.

Since dPCR was more sensitive in detecting persistent CML, it could improve the management of TKI therapy. Further development of this technique could mean that only patients who were truly in deep remission would stop TKI therapy.

“We conclude that dPCR for BCR-ABL1 DNA is the most sensitive available method of residual disease detection in CML and may prove useful in the management of TKI withdrawal,” stated Jane F. Apperley, MD, PhD, FRCPath, department head of the Centre for Haematology at Imperial College, London, England, and lead author of the study.

“If validated in clinical trials of stopping TKIs, this technique will permit a more personalized approach to recommendations for dose reduction or drug cessation in individual patients, ensuring that therapy is withdrawn only from patients with the highest chance of long-term remission.”


1. Alikian M, Ellery P, Forbes M, et al. Next-generation sequencing-assisted DNA-based digital PCR for a personalized approach to the detection and quantification of residual disease in chromic myeloid leukemia in patients. J Mol Diagn. 2016;18(2):176-189.