Digital droplet PCR as a predictive tool for successful discontinuation outcome in chronic myeloid leukemia: Is it time to introduce it in the clinical practice?

Tyrosine kinase inhibitors (TKIs) have drastically changed the outcome of chronic myeloid leukemia (CML) patients. A sustained and deep molecular response achieved over time paves the way to therapy discontinuation, and is a pre-requisite to attempt treatment-free remission. Monitoring of the molecular response during treatment discontinuation is routinely carried out by RQ-PCR, but it may not be the optimal tool to monitor minimal residual disease at the time of stopping treatment and during treatment discontinuation. Different digital PCR platforms (such as droplet dPCR) are available, a method based on water-emulsion droplet technology in which the sample is partitioned into 20,000 droplets and PCR amplification of the template subsequently occurs in each individual droplet. The consequent high sensitivity and precision with a very reliable quantification without the need of a calibration curve and the exquisite reproducibility makes this procedure as an ideal alternative method for the detection of very low levels of disease. Aim of this review is to describe and discuss the recent use of dPCR/ddPCR in CML, focusing in particular on its role in TKI treatment discontinuation strategies.