Minimal Residual Disease Assessment Within the Bone Marrow of Multiple Myeloma: A Review of Caveats, Clinical Significance and Future Perspectives

Abstract

There is an increasing clinical interest in the measure and achievement of minimal residual disease (MRD) negativity in the bone marrow of Multiple Myeloma (MM) patients, as defined equally either by Multicolor Flow Cytometry (MFC) or by Next Generation Sequencing (NGS) technologies. At present, modern technologies allow to detect up to one on 104 or on 105 or even on 106 cells, depending on their throughput. MFC approaches, which have been progressively improved up to the so-called Next Generation Flow (NGF), and NGS, which proved clear advantages over ASO-PCR, can detect very low levels of residual disease in the BM. These methods are actually almost superimposable, in terms of MRD detection power, supporting the lack of unanimous preference for either technique on basis of local availability. However, some technical issues are still open: the optimal assay to use to detect either phenotype (e.g., next generation multidimensional flow cytometry, imaging) or genotype aberrations (e.g., ASO-RQ PCR, digital droplet PCR, NGS) and their standardization, the sample source (BM or peripheral blood, PB) and its pre-processing (red-cell lysis vs. Ficoll, fresh vs. frozen samples, requirement of CD138+ cells enrichment). Overall, MRD negativity is considered as the most powerful predictor of favorable long-term outcomes in MM and is likely to represent the major driver of treatment strategies in the near future. In this manuscript, we reviewed the main pitfalls and caveats of MRD detection within bone marrow in MM patients after front-line therapy, highlighting the improving of the currently employed technology and describing alternative methods for MRD testing in MM, such as liquid biopsy.

Implications and outcomes of MRD‐negative multiple myeloma patients with immunofixation positivity

“…Where conventional complete response (CR) used to signify attainment of the deepest response to therapy, we now have tools including next generation sequencing (NGS) and multi-parametric flow cytometry (MFC) that have allowed for further disease stratification. 1,2 Assessment for minimal residual disease (MRD) has allowed for the detection of greater variability in depth of response, with multiple studies demonstrating inferior outcomes among those with residual tumor cells. 3,4 While evaluation of MRD has significantly advanced myeloma disease prognostication, its utility remains confined to evaluation of disease in the bone marrow (BM).…”

“…We found allelic heterogeneity in eQTL of S100B, encoding a damage-associated molecular pattern molecule. 2 The A alleles of the tag single nucleotide polymorphisms (SNPs) of the eQTL, rs2154586 and rs2070435, both associated with higher S100B gene expression. The A allele of the former SNP associated with AVN whereas the A allele of the latter SNP with reduced rather than increased acute pain episodes.…”

Microfluidic Isolation of Aptamers with Affinity towards Multiple Myeloma Monoclonal Immunoglobulins (M-Ig)

“…i.e., the presence of small numbers of myeloma cells in a patient's body 8 , have better survival than those who are MRD positive 9 . Detection and monitoring of MRD, and thus the M-Ig, is hence emerging as a cornerstone in selecting and guiding therapeutic strategies 10 .…”

Diagnostic deep‐targeted next‐generation sequencing assessment of TP53 gene mutations in multiple myeloma from the whole bone marrow

“…However, TP53 mutation analysis in MM is not widely performed in diagnostics, particularly due to technical limitations regarding sample collection and plasma cell (PC) enrichment. The pitfalls are mainly connected with inter‐individual variability in the sample amount, PC infiltration in bone marrow (BM), PC immunophenotypes and time‐dependent losses of surface markers as well as haemodilution, patchy or site varied PC distribution, aspirate pull order and aggregation of PC in aspirated BM (Mansilla et al , ; Romano et al , ), all together resulting in low PC recovery in some patients.…”