Assessment of plasma cell myeloma minimal residual disease testing by flow cytometry in an international inter‐laboratory study: Is it ready for primetime use?

Abstract

Background Minimal/measurable residual disease (MRD) testing by flow cytometry (FC) has been proposed as a potential surrogate clinical endpoint in plasma cell myeloma (PCM) clinical trials. As a result, effort has gone into standardizing this approach on PCM patients. Aims To assess inter‐laboratory variation in FC MRD testing of PCM patients in an independent inter‐laboratory study. Methods A dilution series of five stabilized bone marrow samples manufactured to contain 0%, 0.1%, 0.01%, 0.001%, and 0.0001% neoplastic plasma cells (PCs) were tested blind, using standardized FC PCM MRD assays by 10 international laboratories. Results Laboratories' assays broadly adhered to the consensus guidelines; however, some deviations were identified in panel design, fluorochrome conjugates, and lysis reagents. Despite this, all laboratories that returned results detected neoplastic PCs down to 0.001% of leucocytes. 6/8 laboratories detected neoplastic PCs at a level of 0.0001%. Quantitative data returned by laboratories showed good consensus and linearity with increasing variation at lower levels of MRD. However, examples of analytical and post analytical error were identified. Summary/Conclusion Broadly standardized PCM MRD FC assays can attain the lower limit of detection (LOD) required by current and future clinical trials, an important consideration in establishing PCM MRD testing as a surrogate clinical marker in PCM clinical trials. Laboratories' assays showed good linearity, encouraging the prediction of survival based on log reduction in neoplastic PC populations in future clinical trials. However, the deviations from consensus guidelines identified in this study would suggest that if PCM MRD assays are further standardized interlaboratory variation could be reduced. © 2018 International Clinical Cytometry Society

Issue Highlights – May 2019

“…This is clearly highlighted in this issue in the work presented by Scott et al , who report on the high sensitivity and good linearity observed in an International Inter‐Laboratory Study based on dilutional series of MM samples. Overall, high (but variable) sensitivity was observed among the participating centers, with good linearity, associated with greater levels of variability for low vs higher PC numbers . Of note, despite the fact that the participating laboratories were all experienced laboratories, deviations from consensus recommendations in panel design, fluorochrome conjugates, lysing reagents occurred, in parallel to specific analytical and post‐analytical errors.…”

“…Overall, high (but variable) sensitivity was observed among the participating centers, with good linearity, associated with greater levels of variability for low vs higher PC numbers (21). Of note, despite the fact that the participating laboratories were all experienced laboratories, deviations from consensus recommendations (22)(23)(24) in panel design, fluorochrome conjugates, lysing reagents occurred, in parallel to specific analytical and post-analytical errors.…”

“…In order to be able to translate these results into routine practice at distinct laboratories, standardization is mandatory (19). This is clearly highlighted in this issue in the work presented by Scott et al (21), who report on the high sensitivity and good linearity observed in an International Inter-Laboratory Study based on dilutional series of MM samples.…”

“…In order to be able to translate these results into routine practice at distinct laboratories, standardization is mandatory . This is clearly highlighted in this issue in the work presented by Scott et al , who report on the high sensitivity and good linearity observed in an International Inter‐Laboratory Study based on dilutional series of MM samples. Overall, high (but variable) sensitivity was observed among the participating centers, with good linearity, associated with greater levels of variability for low vs higher PC numbers .…”

Issue Highlights – September 2020

“…To achieve the sensitivities of 10 ‐5 ‐ 10 ‐6 required for MRD assessment, more cells than can normally be obtained from 100 μL of blood or bone marrow are required (4). Laboratories have developed several methods to obtain the 5‐10 x 10 6 cells per tube required for MRD assays but a standardized approach is needed (5). One method, the bulk lyse approach, described by the EuroFlow Consortium has become the de facto standard (6), but in comparison to routine methods it is labor intensive.…”