Utility Of 9-Color, 11-Parameter Flow Cytometry For Detection Of Plasma Cell Neoplasms: A Comparison With Bone Marrow Morphologic Findings and Concurrent M-Protein Studies In Serum and Urine

Multiparameter flow cytometry (MFC) is a widely available laboratory platform used for primary diagnosis of mature B-cell and plasma cell (PC) neoplasms. Ongoing advances in myeloma therapeutics have drawn attention to the need for advanced laboratory methods for monitoring disease response and defining disease eradication. Recent literature indicates that achievement of remission based on sensitive MFC criteria is prognostically superior to remissions defined by older criteria based on monitoring of paraproteins in blood and urine. As such, the International Myeloma Working Group (IMWG) recommends MFC for minimal residual disease (MRD) testing during clinical trials for multiple myeloma (MM). This study validates a sensitive 9-color, 11-parameter, two-tube MFC assay suitable for both the initial diagnosis of patients with paraproteinemias and MRD monitoring in MM.

We established and validated a 9-color, 11-parameter MFC assay in our laboratory. The 9-color tube contained cytoplasmic κ/cytoplasmic λ/CD45/CD38/CD56/CD138/CD19/CD117/CD20. Results of the MFC were compared to bone marrow microscopic examinations, immunohistochemical (IHC) studies and serum/urine M-protein measurements ordered on 363 samples from patients with documented or suspected PC neoplasms and IgM paraproteinemias.

Total preparation time is approximately 90 minutes (“hands-on” time under 30 minutes) for up to 3 concurrent specimens. The assay is performed in two tubes (control and PC panel) with analysis of up to 1.8 x 10⁶ total bone marrow cells/tube. The mean instrument analysis time was ∼5 minutes/tube (range 1-9 minutes). MFC detected clonal PCs in 19% and 23% of cases in which IHC or morphologic evaluation, respectively, failed to show a clonal plasma cell population. The MFC assay consistently detected clonal PC in bone marrow aspirates when serum M-protein levels were above 1g/dl. The frequency of clonal PC detection by MFC fell in concert with M-protein levels. However, in 11% of patients, MFC detected clonal PC after serum and urine immunofixation studies turned negative.

We conclude that the assay described herein is suitable when immunologic studies are indicated for either primary diagnosis or MRD detection in PC neoplasms. It equals or exceeds sensitivities reported in the literature and it is readily integrated into a high volume, multipurpose clinical flow cytometry laboratory.

Keren: Sebia, Inc (Norcross, GA). : Consultancy.