Evaluation of multiple myeloma measurable residual disease by high sensitivity flow cytometry: An international harmonized approach for data analysis

Abstract

Background Multiple myeloma (MM) measurable residual disease (MRD) evaluated by flow cytometry is a surrogate for progression‐free and overall survival in clinical trials. However, analysis and reporting between centers lack uniformity. We designed and evaluated a consensus protocol for MM MRD analysis to reduce inter‐laboratory variation in MM MRD reporting. Methods Seventeen participants from 13 countries performed blinded analysis of the same eight de‐identified flow cytometry files from patients with/without MRD using their own method (Stage 1). A consensus gating protocol was then designed following survey and discussions, and the data re‐analyzed for MRD and other bone marrow cells (Stage 2). Inter‐laboratory variation using the consensus strategy was reassessed for another 10 cases and compared with earlier results (Stage 3). Results In Stage 1, participants agreed on MRD+/MRD− status 89% and 68% of the time respectively. Inter‐observer variation was high for total numbers of analyzed cells, total and normal plasma cells (PCs), limit of detection, lower limit of quantification, and enumeration of cell populations that determine sample adequacy. The identification of abnormal PCs remained relatively consistent. By consensus method, average agreement on MRD− status improved to 74%. Better consistency enumerating all parameters among operators resulted in near‐unanimous agreement on sample adequacy. Conclusion Uniform flow cytometry data analysis substantially reduced inter‐laboratory variation in reporting multiple components of the MM MRD assay. Adoption of a harmonized approach would meet an important need for conformity in reporting MM MRD for clinical trials, and wider acceptance of MM MRD as a surrogate clinical endpoint.

Utility of CD229 as novel marker in measurable residual disease assessment in multiple myeloma—An evidence‐based approach

“…At present, combined assessment of CD138 and CD38, together with CD45, FSC, and SSC, is considered the standard approach for the identification and gating of PC compartments. [12][13][14] However, in recent years new therapeutic antibodies against a variety of molecules expressed on the surface of PC, including CD38 and CD138, have been developed and are currently under evaluation for the treatment of MM patients. There is therefore a demand for identification of novel markers as potential candidates for MFC based identification and characterisation of PCs.…”

“…Accurate identification of PC and their clear‐cut discrimination from other bone marrow cells is a critical requirement for diagnosis and response assessment of MM and related PCPDs by flow cytometry. At present, combined assessment of CD138 and CD38, together with CD45, FSC, and SSC, is considered the standard approach for the identification and gating of PC compartments 12–14 . However, in recent years new therapeutic antibodies against a variety of molecules expressed on the surface of PC, including CD38 and CD138, have been developed and are currently under evaluation for the treatment of MM patients.…”

Impact of red blood cell lysing on rare event analysis

“…Red cell lysing solutions are specifically designed to decrease potential damage and cell loss. Harmonization efforts have been conducted in this way for clinical and immunological studies [42,43]. However, pathological samples may have increased sensibility to erythrolytic solutions, based on pathology altered cell distribution, received therapy, experimental treatment for relapsed and refractory neoplasia, among others, which can affect whole blood counts, and more importantly when leukopenia samples are needed for diagnosis purposes.…”

“Friends and foes” of multiple myeloma measurable/minimal residual disease evaluation by next generation flow

“…Finally, given the peculiarity of flow-cytometry analysis a high personnel expertise is essential in order to obtain reliable results, especially in demanding cases in which anti-CD38 therapy, presence of different pathologic clones or presence of normal PCs, together with low MRD burden, could lead to bias ( 69 ). Reducing the subjectivity in data analysis requires the work of experienced laboratories, that are constantly monitored and trained, and whose results could be assessed and tested by external quality assurance programs and interlaboratory comparisons.…”