Comprehensive characterization of circulating and bone marrow-derived multiple myeloma cells at minimal residual disease

Abstract

The presence or absence of minimal residual disease (MRD) in patients with multiple myeloma (MM) has emerged as a useful marker to determine the depth of remission. MRD negativity as an endpoint has been shown to be associated with improved progression-free survival in many studies. MRD detection is therefore part of numerous clinical trial protocols for MM. At the present time, two methodologies are most widely accepted for MRD detection: (1) multicolor flow cytometry and (2) next-generation sequencing-based clonotype detection. While both of those methodologies enable accurate quantification of MRD in the bone marrow (BM), with sensitivity as low as 10 to 10, there are several limitations to these methods. First, these approaches reveal the presence or absence of MRD but provide limited molecular information about MM. More comprehensive characterization of MM cells at the MRD stage may identify molecular mechanisms of drug resistance. Second, MRD detection in the BM is typically performed at one time point only, but more frequent detection may define the duration of the MRD status and thus refine its prognostic value. Third, less-invasive approaches that avoid the discomfort and risk associated with BM biopsy would be highly desirable, especially in elderly or frail patients. "Liquid biopsy" for the detection and characterization of circulating MM cells may address these issues. Although MRD detection in the peripheral blood at the same sensitivity as in the BM may be challenging, the identification of patients who do not achieve MRD negativity might reduce the need for BM biopsies. Here, we give an overview of approaches that have been described to detect and characterize MM cells when they occur at very low frequencies in the peripheral blood or in the BM, emphasizing recently described next-generation sequencing approaches for more comprehensive characterization of circulating MM cells.

Blood monitoring of circulating tumor plasma cells by next generation flow in multiple myeloma after therapy

“…The workup of patients who present with cytopenia(s) can be extensive, given the wide differential diagnosis. 1 Although only a minority of patients are ultimately diagnosed with a hematologic malignancy, a key entity to exclude in this differential is myelodysplastic syndrome (MDS), 2 which requires bone marrow morphology and cytogenetics for diagnosis. There is a clinical need for the development of minimally invasive ancillary tests to enhance conventional hematologic workup (eg, complete blood count with differential, B12/folate testing, iron-related studies, and serum protein electrophoresis) in the identification of patients who are at a low risk of having an underlying hematologic malignancy as the cause of cytopenia(s), thereby avoiding a costly and invasive bone marrow biopsy (BMBx).…”

“…In recent years, detection of circulating tumor plasma cells (CTPC), tumor cell-derived deoxyribonucleic acid (DNA), RNA, or protein markers in blood has gained interest for disease monitoring in multiple myeloma (MM). 1,2 This is mainly because of (1) the minimally invasive nature of blood vs bone marrow (BM) analyses, (2) the possibility for more precise quantification of absolute numbers of CTPC than BM minimal residual disease (MRD) resulting from absence of potential hemodilution, and (3) the (nonlinear) correlation observed between CTPC numbers and BM disease burden at diagnosis. 1,3 Recently, we have shown by high-sensitivity next-generation flow (NGF) that CTPC are systematically present in blood of MM at diagnosis, with an adverse prognostic impact for higher counts.…”

“…1,2 This is mainly because of (1) the minimally invasive nature of blood vs bone marrow (BM) analyses, (2) the possibility for more precise quantification of absolute numbers of CTPC than BM minimal residual disease (MRD) resulting from absence of potential hemodilution, and (3) the (nonlinear) correlation observed between CTPC numbers and BM disease burden at diagnosis. 1,3 Recently, we have shown by high-sensitivity next-generation flow (NGF) that CTPC are systematically present in blood of MM at diagnosis, with an adverse prognostic impact for higher counts. 3 These results highlight the relevance of greater levels of disease dissemination via blood in conferring a malignant behavior to MM, suggesting the presence of blood CTPC might be required for subsequent disease progression of treated MM patients.…”

Detection of Circulating Tumor Plasma Cells in Monoclonal Gammopathies: Methods, Pathogenic Role, and Clinical Implications

“…However, blood monitoring of CTPC has multiple advantages compared to BM MRD. Thus, detection/quantitation of CTPC in blood is a minimally-invasive approach that, unlike BM MRD, is not affected by (patchy) disease distribution and/or hemodilution [ 148 ]. At the same time, it is well-suited for (more) frequent monitoring of newly-diagnosed MGUS and treated MM patients who attain complete response [ 21 , 32 , 35 , 118 ], providing information that is complementary to serum immunofixation [ 35 ], for example, for the follow-up of non-secretory PC tumors [ 129 ].…”

Monitoring minimal residual disease in the bone marrow using next generation sequencing

“…Furthermore, a single bone marrow aspirate will not fully capture the spatial heterogeneity of multiple myeloma. Thus, going forward, still smaller quantities of disease within the patient can only be detected by combining bone marrowbased MRD testing with other modalities, such as imaging and blood-based assays (46)(47)(48)(49)(50)(51).…”