Multiparametric Flow Cytometry for MRD Monitoring in Hematologic Malignancies: Clinical Applications and New Challenges.

Giovanni Riva,Mario Luppi,Fabio Forghieri,Enrico Tagliafico,Beatrice Lusenti,Anna Maria Ottomano,Patrizia Comoli,Vincenzo Nasillo,Rossana Maffei,Silvia Martinelli,Patrizia Barozzi,Stefania Fiorcari,Leonardo Potenza,Tommaso Trenti,Roberto Marasca,Giuliano Bergonzini,Rossella Manfredini,Ambra Paolini,Ivana Lagreca

doi:10.3390/cancers13184582

Abstract

Simple SummaryIn hematologic cancers, Minimal Residual Disease (MRD) monitoring, using either molecular (PCR) or immunophenotypic (MFC) diagnostics, allows the identification of rare cancer cells, readily detectable either in the bone marrow or in the peripheral blood at very low levels, far below the limit of classic microscopy. In this paper, we outlined the state-of-the-art of MFC-based MRD detection in different hematologic settings, highlighting main recommendations and new challenges for using such method in patients with acute leukemias or chronic hematologic neoplasms. The combination of new molecular technologies with advanced flow cytometry is progressively allowing clinicians to design a personalized therapeutic path, proportionate to the biological aggressiveness of the disease, in particular by using novel immunotherapies, in view of a modern decision-making process, based on precision medicine.Along with the evolution of immunophenotypic and molecular diagnostics, the assessment of Minimal Residual Disease (MRD) has progressively become a keystone in the clinical management of hematologic malignancies, enabling valuable post-therapy risk stratifications and guiding risk-adapted therapeutic approaches. However, specific prognostic values of MRD in different hematological settings, as well as its appropriate clinical uses (basically, when to measure it and how to deal with different MRD levels), still need further investigations, aiming to improve standardization and harmonization of MRD monitoring protocols and MRD-driven therapeutic strategies. Currently, MRD measurement in hematological neoplasms with bone marrow involvement is based on advanced highly sensitive methods, able to detect either specific genetic abnormalities (by PCR-based techniques and next-generation sequencing) or tumor-associated immunophenotypic profiles (by multiparametric flow cytometry, MFC). In this review, we focus on the growing clinical role for MFC-MRD diagnostics in hematological malignancies—from acute myeloid and lymphoblastic leukemias (AML, B-ALL and T-ALL) to chronic lymphocytic leukemia (CLL) and multiple myeloma (MM)—providing a comparative overview on technical aspects, clinical implications, advantages and pitfalls of MFC-MRD monitoring in different clinical settings.

Highlights

Since the last decades of the past century, the development of affordable and sensitive methods to identify rare leukemic cells, still detectable—at very low levels—either in the bone marrow (BM) or in the peripheral blood (PB) of hematologic patients on posttreatment follow-up, has provided a striking improvement of our ability to quantify the resistant/recurrent disease burden, far beyond morphologic remission
According to guidelines: (i) Minimal Residual Disease (MRD) testing is not indicated in routine clinical practice, (ii) in clinical trials MRD should be evaluated in all responding patients, either in partial response (PR) or complete response (CR), at least in PB, (iii) U-MRD status documented on PB should be confirmed on BM, (iv) there is no specific recommendation to support the choice of a validated assay over another, since both MFC and molecular techniques (RQ-PCR, droplet digital PCR and high throughput sequencing) are considered adequate to assess MRD at the required threshold; the assay choice depends on the rationale for MRD determination and local availability [75,77]
The high prognostic significance of MRD detection has shown a remarkable impact on the therapeutic management of hematologic patients

Summary

Introduction

Since the last decades of the past century, the development of affordable and sensitive methods to identify rare leukemic cells, still detectable—at very low levels—either in the bone marrow (BM) or in the peripheral blood (PB) of hematologic patients on posttreatment follow-up, has provided a striking improvement of our ability to quantify the resistant/recurrent disease burden, far beyond morphologic remission (i.e., below the conventional microscopy threshold of 1 out of 100 cells). In addition to the basic set of phenotypic markers, MFC-MRD monitoring can be extended to the investigation of other relevant antigens, which have shown some promising uses for diagnostic definition and prognostic assessment, as well as for therapeutic applications.

Results

Conclusion