Minimal Residual Disease Assessment

What is minimal residual disease (MRD) and how can MRD assessment be used in clinical trials?

MRD is the small number of malignant cells that remain in the patient during or after cancer treatment.²

MRD has potential application as a versatile biomarker: ³

Prognostic – to identify the likelihood of a clinical event independent of treatment.
Predictive – to predict the likelihood of response to a particular treatment.
Monitoring – to detect changes in the degree or extent of disease.
Efficacy/response – to measure the response to drug exposure.

To be effective, MRD analysis must be reliable and achieve adequate accuracy in: ⁴

Specificity – distinguish normal cells from malignant cells.
Sensitivity – detect malignant cells within the context of normal cells.
Reproducibility – have appropriate standardisation of methods.

MRD functions as a valuable biomarker in a range of clinical trial scenarios

For blood cancers such as acute lymphoblastic leukaemia, and bone marrow cancers such as multiple myeloma, MRD is a fundamental prognostic factor.¹

Additionally, as MRD has been regarded as an important prognostic factor for predicting disease recurrence, it can also be used as a stratification tool to select patients at high risk, guide allocation into specific treatment arms and to enrich the trial population.³

MRD kinetics can also be used to provide insights into responses to chemotherapy, stem cell transplantation, and possibly immunotherapies.²

In the future, MRD could be used in efficacy trials as a surrogate endpoint, to predict a specific clinical outcome of a patient, due to its potential for integrating different aspects of treatment efficacy.^2,3

To realise the potential of this biomarker, the correlation between MRD and clinical outcome must be established for each disease setting and drug.

What are the comparative advantages of Next Generation Flow™ for minimal residual disease detection?

Conventional cytomorphology techniques such as microscopy that are usually used to define patient complete remission for haematologic malignancies have a detection limit of 5%, around one tumour cell in 100^2,3and are therefore not sufficient to detect MRD, which exists at orders of magnitude below the limit of conventional morphologic detection

A range of available technologies, each with their own advantages and disadvantages, play a role in MRD assessment:

Quantitative polymerase chain reaction has been extensively used as the molecular gold-standard approach to detect MRD levels in lymphoid malignancies; however, it is a labour-intensive technique, requiring the construction of a standard curve for every patient, and is only applicable for 40–75% of myeloma patients.⁵

Droplet digital PCR (ddPCR) is an advanced method in which each sample is divided into droplets and each one is analysed individually so small changes in fluorescence intensity are more easily detected. It has the potential to identify clonal evolutions and allows the quantitation of nucleic acid targets without the need of the calibration curves.⁶

Next generation sequencing offers sensitivities from 10⁻⁴ to 10⁻⁷ and eliminates some of the time-consuming optimisation steps needed in PCR⁶; however, sophisticated bioinformatic analysis means turnaround times are still in the region of one week and a standardised method is lacking.⁶

Multiparametric flow cytometry is a less labour-intensive and faster method than PCR for detecting MRD, which is based on the discrimination of malignant cells from normal cells by identifying aberrant immunophenotypes

This technique is based on the simultaneous recognition of several phenotypic markers and the capacity to analyse large numbers of cells in a few minutes.¹

Detection limits are not far from the most sensitive molecular techniques.¹

Next Generation Flow™ represents the next step in the technological evolution of flow cytometry techniques with substantial improvement of high-throughput flow approach.¹

This technique makes it possible to rapidly acquire several millions of cells (>10⁷) and therefore reach the sensitivity of molecular methods (10^-6).¹

Standardisation of most of the steps of the process, coupled with innovative software tools, yields accurate, reproducible and objective results.¹

References

Riva G, Nasillo V, Ottomano AM, et al. Multiparametric Flow Cytometry for MRD Monitoring in Hematologic Malignancies: Clinical Applications and New Challenges. Cancers (Basel) 2021;13:4582.
Brüggemann M, Kotrova M. Minimal residual disease in adult ALL: technical aspects and implications for correct clinical interpretation. Blood Adv 2017;1:2456-2466.
United States Food and Drug Administration. Hematologic Malignancies: Regulatory Considerations for Use of Minimal Residual Disease in Development of Drug and Biological Products for Treatment.; 2020.
Van Dongen JJM, van der Velden VHJ, Brüggemann M, et al. Minimal residual disease diagnostics in acute lymphoblastic leukemia: need for sensitive, fast, and standardized technologies. Blood 2015;125:3996-4009.
Medina A, Puig N, Flores-Montero J, et al. Comparison of next-generation sequencing (NGS) and next-generation flow (NGF) for minimal residual disease (MRD) assessment in multiple myeloma. Blood Cancer J 2020;10:108.
Contreras Yametti GP, Ostrow TH, Jasinski S, et al. Minimal Residual Disease in Acute Lymphoblastic Leukemia: Current Practice and Future Directions. Cancers (Basel) 2021;13:1847.

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