“MRD measurement is now a key feature of CLL clinical trials reporting. It can change CLL care by enabling approval of medication use in the wider (nontrial) patient population based on MRD data, without having to wait (ever-increasing) times for conventional trial outcomes, such as progression-free survival [PFS],” said study author Tahla Munir MD, of the department of hematology, at the Leeds (England) Teaching Hospitals of the National Health Service Trust.
courtesy of NHS
Dr. Tahla Munir
“It also has potential to direct our treatment duration and follow-up strategies based on MRD results taken during or at the end of treatment, and to direct new treatment strategies, such as intermittent (as opposed to fixed-duration or continuous) treatment,” Dr. Munir said in an interview.
The review study defined MRD according to the detectable proportion of residual CLL cells. (Current international consensus for undetectable is U-MRD4 1 leukemic cell in 10,000 leukocytes.) The advantages and disadvantages of different MRD assays were analyzed. Multiparameter flow cytometry, an older technology, proved less sensitive to newer tests. It is reliable measuring to a sensitivity of U-MRD4 and more widely available than next-generation real-time quantitative polymerase chain reaction tests (NG-PCR).
“NG-PCR has the most potential for use in laboratory practice. It doesn’t require patient-specific primers and can detect around 1 CLL cell in 1x106 leukocytes. The biggest challenge is laboratory sequencing and bioinformatic capacity,” said lead study author Amelia Fisher, clinical research fellow at the division of cancer studies and pathology, University of Leeds.
“Multiple wells are required to gather adequate data to match the sensitivity of NGS. As this technology improves to match NGS sensitivity using fewer wells, once primers (bespoke to each patient) are designed it will provide a simple to use, rapid and easily reportable MRD tool, that could be scaled up in the event of MRD testing becoming routine practice,” explained Dr. Fisher.
The study also demonstrated how MRD can offer more in-depth insights into the success of treatments versus PFS. In the MURANO clinical trial, which compared venetoclax-rituximab treatment with standard chemoimmunotherapy (SC) to treat relapsed or refractory CLL, the PFS and overall survival (OS) remained significantly prolonged in the VR group at 5 years after therapy.
Analysis of MRD levels in the VR arm demonstrated that those with U-MRD4 had superior OS, with survival at 5 years of 95.3%, compared with those with higher rates of MRD (72.9%). A slower rate of MRD doubling time in the VR-treated patients, compared with the SC-treated patients, also buttressed the notion of moving from SC to VR treatment for the general CLL patient population.
Researchers cautioned that “a lot of the data is very recent, and therefore we do not have conventional trial outcomes, e.g., PFS and OS for all the studies. Some of the data we have is over a relatively short time period.”
University of Texas MD Anderson Cancer Center
Dr. Alessandra Ferrajoli
An independent expert not associated with the study, Alessandra Ferrajoli, MD, associate medical director of the department of leukemia at the University of Texas MD Anderson Cancer Center, Houston, expressed agreement with the study’s main findings.
“It is very likely that MRD assessment will be incorporated as a standard measurement of treatment efficacy in patients with CLL in the near future. The technologies have evolved to high levels of sensitivity, and the methods are being successfully harmonized and standardized,” she said.
Neither the study authors nor Dr. Ferrajoli reported conflicts of interest.