The clinical application of BCR::ABL1 digital polymerase chain reaction (PCR) testing may reliably quantify stable deep molecular remission in patients with chronic myeloid leukemia (CML), which could help determine when maintenance therapy may be discontinued successfully, according to a recent Dutch study published by Kockerols et al in The Journal of Molecular Diagnostics. The transcript unique for CML may be more sensitive and accurate compared with the current standard, real-time quantitative PCR in detecting ultralow levels of residual leukemic disease.
Background
BCR::ABL1—a specific genetic fusion protein that is characteristic of CML—is created when the BCR and ALB1 genes become abnormally joined together. With targeted therapy using tyrosine kinase inhibitors (TKIs), patients with CML may achieve deep molecular responses. Those who reach this depth of remission may have a normal life expectancy and qualify for TKI discontinuation.
Study Methods and Results
In a nationwide, prospective multicenter study, researchers collected 168 samples from 136 Dutch patients with CML who were being considered for TKI discontinuation from July 2020 until the time of analysis in May 2023.
“BCR::ABL1 digital PCR was found to accurately quantify BCR::ABL1 around the level of 0.0023% on the International Scale, which is the clinically relevant prediction cutoff in the context of treatment-free remission. The target sensitivity was set at MR5.0, requiring reliable detection of one transcript in a background of at least 100,000 regular copies. This was achieved in 97% of [the samples of patients in deep molecular remission]. Digital PCR was able to detect and quantify the BCR::ABL construct in 68% of samples below the limit of detection of current standard [real-time quantitative PCR],” detailed senior study author Peter E. Westerweel, MD, PhD, of the Department of Internal Medicine at the Albert Schweitzer Hospital in the Netherlands. “Digital PCR was therefore more sensitive and more accurate, allowing a reliable measurement to select patients [with CML] in deep remission eligible for drug treatment discontinuation,” he indicated.
In addition, the researchers noted that there was a variance in the fluorescence level of droplets rendered by the digital PCR technique as a result of a difference in transcript type carried by individual patients. Droplets with higher fluorescence contained the target transcript type and were considered positive, whereas droplets with lower fluorescence were considered negative.
“Some patients have a so-called e13a2 transcript type, while other [patients] have an e14a2 transcript type. We validated that the assay can be used to identify the transcript type in patients with detectable disease. This additional discovery is very relevant as we have previously shown that the transcript type is a risk factor for molecular relapse after drug discontinuation. Often, the transcript type is not known for patients and cannot be established using standard techniques once patients are in deep remission,” emphasized Dr. Westerweel.
Conclusions
The digital PCR for BCR::ABL in this study used a U.S. Food and Drug Administration–approved, commercially available assay, which made general use feasible. The technology may improve the management of CML by enabling more precise monitoring of measurable residual disease and greater risk assessment among patients in managing treatment-free remission.
“Digital PCR for BCR::ABL is a valuable and reliable tool to aid clinical decision-making in [patients with] CML,” concluded Dr. Westerweel.
Disclosure: For full disclosures of the study authors, visit jmdjournal.org.
