What’s Next for MRD in Myeloma?

By Leah Lawrence - Last Updated: May 31, 2023

Current techniques to monitor measurable residual disease (MRD) in patients with multiple myeloma (MM) often test bone marrow aspirates, but the noninvasive nature of testing peripheral blood is drawing the interest of researchers.

MRD is one of the best available prognostic markers for patients with MM, according to Bruno Paiva, PharmD, PhD, Co-Director of the Flow Cytometry Platform and the Monoclonal Gammopathies Research Laboratory at the Clínica and CIMA Universidad de Navarra in Spain.

In 2016, the International Myeloma Working Group (IMWG) incorporated MRD measurement into its uniform response criteria to better identify responses that were deeper than what was traditionally defined as a complete response.1 Current techniques to measure MRD most commonly test bone marrow aspirates.

However, there is growing interest in researching whether there are methods of measurement sensitive enough to assess MRD in the peripheral blood, a less invasive approach that could allow for more frequent monitoring.

“You have to keep in mind, though, that despite more than a decade of top-quality research into MRD in myeloma [measured in bone marrow], with several manuscripts reported by many different groups and pharmaceutical companies, all showing very reproducible, solid data, a lot of questions about the use of MRD remain,” Dr. Paiva said.

“For MRD measurement in the blood, we are definitely only at the beginning, and, similar to bone marrow, I foresee a decade of intensive research prior to knowing how and when to use MRD in the blood.”

Where Things Stand

Currently, it is not considered standard of care to check MRD in patients with MM, explained Swathi Namburi, MD, of the Swedish Cancer Institute in Seattle, Washington.

“There are reasons to check it and reasons not to check it,” Dr. Namburi said. “I consider the patient’s goals of care and what treatment plan they are eligible for to see if MRD testing should be incorporated into a typical diagnostic algorithm.”

There is currently only one US Food and Drug Administration (FDA)-approved test to detect MRD in patients with myeloma: the next-generation, sequencing-based clonoSEQ assay, which measures MRD in bone marrow. Approved in 2018, the clonoSEQ assay is capable of detecting MRD at levels below one in 1 million cells or 10-6.2 The IMWG currently defines MRD negativity as the absence of clonal plasma cells at a minimum sensitivity of 10-5.

The approval was based on data showing that MRD measured at the start of maintenance therapy was a strong prognostic indicator of progression-free survival (PFS) and overall survival (OS) in patients treated with lenalidomide, bortezomib, and dexamethasone. Patients with MRD negativity had a higher probability of prolonged PFS regardless of treatment approach.3

Although not FDA approved, other techniques of MRD assessment in bone marrow aspirate have been evaluated in clinical trials, including multiparametric flow cytometry (MFC),4 allele-specific oligonucleotide quantitative polymerase chain reaction,5 and, more recently, next-generation flow (NGF) cytometry.6

“[MRD] was a substantial addition to our understanding of how deeply patients can achieve response,” said Andrzej Jakubowiak, MD, PhD, Director of the Myeloma Program at the University of Chicago Medical Center. “We have learned that of our patients who achieve a complete response, only a portion of those patients will be MRD-negative. Currently, up to 60% to 80% of patients can achieve MRD-negativity with the standard sensitivity cutoff of 10-5, but it may only be 40% to 50% with a cutoff of 10-6.”

A meta-analysis has established that MRD negativity in MM was associated with improved PFS and OS in both newly diagnosed and relapsed or recurrent disease, regardless of MRD sensitivity threshold, cytogenetic risk, method of MRD assessment, and depth of clinical response at the time of MRD measurement.7

“Outside of clinical trials, the use of MRD measurement is very physician-, practice-, or patient-dependent,” said Sarah Holstein, MD, PhD, a Professor in the Division of Oncology and Hematology at the University of Nebraska Medical Center. “That is, in part, because MRD has not yet been formally defined as a surrogate endpoint for things like PFS or OS. In addition, it has not been clearly shown that basing treatment decisions off MRD status results in improved outcomes.”

In 2020, the FDA finalized guidance on the use of MRD as a biomarker in clinical trials to support marketing approval of drugs and biological products. The guidance detailed that the relationship between MRD and clinical benefit needed to be demonstrated in multiple disease settings—relapsed, refractory, newly diagnosed, smoldering, nontransplant eligible—to establish MRD as a surrogate endpoint. The guidance also noted the potential issue that MRD assessed using MFC and next-generation sequencing (NGS) in the bone marrow is not able to detect extramedullary disease.8

The Potential of Blood

The ability to detect extramedullary disease could be one of the potential advantages for measuring MRD using peripheral blood, Dr. Paiva said.

“The blood could be more informative than the marrow because it would capture disease coming from different bone marrow sites—not just the one sampled—as well as extramedullary disease sites outside of the bone marrow,” Dr. Paiva said. “This is particularly important in myeloma because the disease is characterized by heterogeneous bone marrow involvement and, less frequently, extramedullary involvement.”

The other potential advantage is the noninvasive nature of testing peripheral blood.

“Bone marrow testing is very difficult for patients; they hate it,” Dr. Jakubowiak said. “It is not sustainable to ask patients to undergo frequent MRD assessment in the bone marrow.”

A method that allows for more frequent testing could potentially better capture MRD kinetics, which could be more informative not only from a prognostic point of view, but also to adjust treatment plans, he said.

The two main methods used for MRD assessment in bone marrow—NGS and NGF—can also be used in the blood; however, because tumor burden in the peripheral blood is lower than in the bone marrow, these methods produce many false-negative results.

For example, one study evaluating flow cytometry in the peripheral blood compared with the bone marrow showed that up to 40% of patients who were MRD-positive in bone marrow had undetectable circulating tumor plasma cells in paired blood samples.9

As a result, methods in development for measuring MRD in peripheral blood need to have increased sensitivity, and progress is being made in this area.


Dr. Paiva together with Laura Notarfranchi, MD, of the Department of Medicine and Surgery at the University of Parma in Italy, and colleagues recently presented data on the use of a new technology they called BloodFlow.10

“The idea is to use NGF, developed by the EuroFlow Consortium, and to increase the sensitivity of the technique by integrating immunomagnetic microbeads targeting CD138 prior to NGF,” Dr. Notarfranchi said.

The method requires a large sample of blood of about 50 mL, Dr. Notarfranchi said. These samples are then magnetically labeled and processed, and about 100-µL aliquots are enriched with circulating plasma cells and analyzed using NGF.

Dr. Notarfranchi and colleagues presented the results of an analysis comparing MRD assessment using BloodFlow with NGF in peripheral blood or bone marrow in 353 samples collected in different treatment scenarios. BloodFlow detected MRD in 9% of samples, with the lowest MRD level at 6×10-8. Of the 33 samples that were MRD-positive with BloodFlow, more than half (58%) were MRD-negative using NGF. All MRD-negative cases on BloodFlow were also negative by NGF.

Concordance of samples was observed in 69% of double-negative samples and 9.5% of double-positive samples. Approximately 20% of samples were MRD-negative in bone marrow but positive in peripheral blood.

“BloodFlow showed a negative predictive value of 77% compared with NGF in marrow,” Dr. Notarfranchi said, adding that they are working to increase the negative predictive value and reduce the number of false negatives in the blood compared with the marrow.

“This two-step process looks promising,” Dr. Holstein said. “The recently presented work suggesting that they could detect levels as low as 6×10-8 is probably where we need to be to confidently say whether or not there are any abnormal plasma cells in the blood.”

Mass Spectrometry

The other technique that has recently shown potential is the use of mass spectrometry as a method to detect the M protein, which is produced by the expanding plasma cell clone in monoclonal gammopathies.

“Mass spectrometry-based evaluation of MRD is, at the moment, at different phases of development,” Dr. Jakubowiak said.

The Mayo Clinic has a commercially available form of mass spectrometry called matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) that is currently included in the IMWG’s recommendations as an accepted method for screening for M proteins.11

A study comparing MALDI-TOF MS in peripheral blood with NGF in bone marrow in 71 patients with MM found concordance between methods for 62% of patients (44/71); eight patients were positive using both methods and 36 were negative for both. An additional 17 patients were detectable only by MALDI-TOF and 10 patients were detectable only by NGF.12 The samples studied were not paired samples.

Another mass spectrometry method being explored is mass spectrometry with liquid chromatography (LC-MS). Dr. Jakubowiak and colleagues published the results of a phase II study analyzing the use of LC-MS, a method that may be more expensive than MALDI-TOF MS but offers increased sensitivity.

In the analysis, they compared mass spectrometry (both LC-MS and MALDI-TOF MS) in the peripheral blood with serum protein electrophoresis/immunofixation, positron emission tomography/computed tomography (PET/CT) imaging, MFC, and NGS in the bone marrow in 76 patients with newly diagnosed MM enrolled in a study of carfilzomib, lenalidomide, and dexamethasone (KRd). MALDI-TOF MS was at least as sensitive as MRD by NGS, with a limit of detection of less than 10-5 in the bone marrow.13

MRD assessment using LC-MS increased sensitivity. For some paired samples, LC-MS was superior to the current standard of MRD negativity, with a limit of detection less than 10-5 and was at least as sensitive as MRD by NGS, with a limit of detection less than 10-6.

A more recent analysis comparing MRD assessment with MALDI-TOF MS and MS-LC in peripheral blood and NGS again showed that LC-MS could possibly exceed the sensitivity of MRD by NGS in the marrow, with a sensitivity threshold of 10-6.14

“Mass spectrometry with or without liquid chromatography has limitations,” Dr. Jakubowiak said. “With this technique—at least at the moment—there is a requirement to have earlier samples where the M protein is still present in reasonable abundance so you can identify the mass of M protein. You have to have that original sample to know that the original M protein is not detectable or substantially reduced.”

Some patients with MM secrete M proteins below a measurable quantity or have no detectable M proteins at all.

Another potential limitation is a phenomenon where the M protein is relatively slow to disappear from the body, Dr. Jakubowiak said. “Mass spectrometry may be detecting a slowly clearing M protein that is otherwise no longer being produced.”

Finding the right time for when mass spectrometry needs to be used requires further investigation.

Potential Applied Use

“It is going to be tricky to figure out how best to use this MRD data as far as clinical intervention goes,” Dr. Namburi said. “This is not like acute leukemia. Patients with MM may have a long period of controlled disease that is MRD-positive, and we are waiting for a true relapse. Intervening too early may expose them to too much therapy without a proven survival benefit. Right now, this should only be done in a clinical trial setting.”

How to best use MRD information has been, and continues to be, explored in a number of studies.

Earlier this year, Dr. Jakubowiak and colleagues published interim results of the phase III ATLAS trial, a comparison of KRd to lenalidomide alone as maintenance therapy after transplant.15 As part of the risk-adapted, MRD-directed design, patients assigned to the triplet who had no detectable MRD at the 10-5 level after cycle 6 and had standard-risk cytogenetics were switched to lenalidomide maintenance at cycle 9. A post-hoc analysis showed a PFS benefit among those patients assigned to KRd who met criteria for de-escalation to maintenance lenalidomide alone.

“We based this strategy on previous results that had generated some preliminary information, and it still requires more validation, but this group of patients had the best outcomes of all patients in the trial,” Dr. Jakubowiak said. “It showed the power of using MRD information for de-escalation of therapy to lower potential toxicity.”

Similarly, the phase II MASTER trial used an MRD response-adapted approach in its analysis of daratumumab plus KRd induction followed by transplant and daratumumab-KRd consolidation. Patients who were MRD-negative at two landmark timepoints were allowed to discontinue treatment and be observed.16

“MRD negativity was high in this study, and they reported that people with standard-risk disease did very well,” Dr. Jakubowiak said. “On the other hand, patients with high-risk disease who discontinued treatment had earlier progression of disease.”

Recently presented results from the MRD2STOP trial also explored the use of multimodal MRD negativity for cessation of therapy after one year of maintenance. In MRD2STOP, for eligibility to discontinue maintenance therapy, MRD was assessed using the clonoSEQ method at the 10-6 level of sensitivity; however, the trial is also assessing the use of CD138-enriched bone marrow aspirates and clonoSEQ to achieve a sensitivity of 10-7 and both MALDI-TOF and LC-MS, as well as cell-free DNA.17

At a median follow-up of 14 months, five of 38 patients had MRD resurgence and two of these five had disease progression. Of the five who progressed, four had a positive MRD at baseline when tested for CD138-enriched samples at the higher, 10-7 sensitivity threshold, suggesting that patients who are MRD-positive at 10-7 sensitivity may be at increased risk for progression if they discontinue therapy.

There are also multiple other ongoing studies evaluating MRD-guided management of MM, including SWOG’s DRAMMATIC trial that will evaluate maintenance lenalidomide with or without daratumumab/rHuPh20 post-transplant, with MRD used to direct therapy duration.18

“These trials should hopefully help us to look at an MRD-negative result and feel fairly confident about what to expect in terms of time until relapse,” Dr. Namburi said. “That is what people want to know when they are dealing with this cancer. What do the next three years look like?”

Multimodal Future

Even with the increased sensitivity of the newer peripheral blood MRD technologies, it is likely that a thorough, accurate assessment of MRD will always include multiple modalities, including imaging, Dr. Paiva said.

“Imaging may not be as sensitive as classical MRD methods, but imaging is very important in a disease like myeloma,” Dr. Paiva said. “PET/CT is more commonly used for evaluating treatment efficacy, and this may be complementary to MRD measured either in the marrow or, eventually, peripheral blood.”

As it stands now, MRD measurement in peripheral blood is not ready to replace bone marrow aspiration, Dr. Notarfranchi said. “However, in the future, in particular settings such as during maintenance or follow-up, we may be able to reduce the number of bone marrow biopsies by integrating BloodFlow or other techniques.”

Dr. Namburi agreed, “As peripheral blood testing gets better, I suspect that we will be looking to the marrow a lot less often … maybe only a few times during the entire myeloma journey. We may be able to test the peripheral blood more routinely—depending on the phase of treatment—but still have defined timepoints where we feel compelled to check marrow.”

Leah Lawrence is a freelance health writer and editor based in Delaware.


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