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The future of CML Testing

New and Advanced Monitoring: q-PCR techniques; can we do even better?

At the moment probably not, but in the future we should expect some changes. The recently published updated ELNet Recommendations and the 2013 edition of the NCCN Guidelines both suggest that strict molecular monitoring by standardised q-PCR testing should be performed at 3, 6, 9 and 12 month time points. A number of international studies that have provided robust evidence that BCR-ABL1 transcripts below 10% by q-PCR, (or 35% Ph+ by cytogenetics) at 3 months and below 1% at 6 months, is predictive of event free survival (EFS) over the longer term.

According to ELNet 2013 recommendations, MMR (0.1% I.S.), as a stable molecular response over the longer term is, in general, a reasonable goal to be achieved within 12 months of starting therapy.

  • A reduction in time taken to report results is important because BCR-ABL1 transcript levels at 3 and 6 months are increasingly used as a basis to drive changes in therapy.

  • A great deal of attention has recently been focused on reaching agreement of a more precise definition of minimal, or measurable, residual disease (MRD) such as MR3, MR4, MR4.5 and MR5

  • More precise definitions of MRD would present a basis to enrol patients in clinical studies leading to dose de-escalation and/or discontinuation with the possibility of remaining in treatment free remission (TFR). Ideally this would be achieved with newer testing methods such as digital q-PCR, a method that does not require a control gene or standardisation, and thus detects BCR-ABL1 transcripts with even greater precision. However, it may not be widely adopted for some years yet.

GeneXpert® System by Cepheid

An automated pre-prepared cartridge based system, requiring only 250 micro-litres of blood per sample.

  • Automatically extracts mRNA from a sample

  • Converts results to the International Standard if required

  • The Adelaide lab has found equivalent sensitivity to the present method

  • A newer version has increased sensitivity even further

  • It can be used for testing for other diseases making its use more cost effective

Digital PCR

  • A newer approach to nucleic acid detection using a different method of absolute quantification and rare allele detection compared to conventional q-PCR

  • Allows researchers to explore beyond the limits of q-PCR

  • It counts individual molecules for absolute quantification by partitioning a sample into many individual real-time PCR reactions. Some portions of the reactions will test positive for the target molecules, others will test negative. Without having to use reference standards or endogenous controls, the fraction of negative answers generates an absolute answer reflecting the exact number of target molecules in a sample.

  • Nevertheless, both technologies are complementary

DNA PCR

The Adelaide lab in Australia is studying DNA PCR, a method that tests at a unique (personalised) DNA level. An assay can be designed to fit an individual patient. DNA PCR is 1 to 1.5 logs more sensitive than conventional q-PCR method using mRNA. It represents a way of identifying patients who can successfully stop treatment without losing response; however it is presently too impractical to use on the wider CML population and remains in the realm of research for now.

Then and Now: the post imatinib era

“Imatinib produced a big breakthrough in the course of CML. Today, after less than 15 years, we know more, we have more, and we want more. If on one hand, we must realistically stay at standard treatment recommendations, on the other hand we should continue to design new treatment protocols and to enrol new patients in prospective studies. This is not easy, because of the high efficacy of standard treatment. In any case, the treatment of CML must be guided by healthcare professionals with specific training and specific interest in CML that are necessary for the optimisation of the treatment and a proper utilisation of the resources. The home physicians must be involved more and more in the care of the CML patient, because an optimal treatment ensures an average life expectancy, and the patient should no longer be considered as a patient at risk of dying of cancer, but as any other individual.”
Michele Baccarani et al, Mediterr J Hematol Infect Dis v.6(1); 2014 -  PMC3894838

Last modified: 
28 July 2015