Immunophenotypic Characterization and Ploidy Analysis of Neoplastic Plasma Cells by Multiparametric Flow Cytometry

Flow cytometric (FCM) immunophenotyping is an important tool for generating diagnostic and prognostic information in plasma cell dyscrasias. This study aimed to evaluate the immunophenotype and ploidy status of plasma cells (PCs) in patients of myeloma and its correlation with other laboratory parameters. Bone marrow of 70 newly diagnosed cases of myeloma were subjected to FCM using a panel of antibodies; CD138, CD38, CD19, CD45, CD28, CD81, CD56, CD200, and CD229. FxCycle Violet (FCV) dye was used for the ploidy analysis of clonal PCs. Median age was 60 years with M:F ratio of 3.2:1. A positive correlation was noted between the morphological and FCM-based PC enumeration (r = 0.4, p = 0.001). Aberrant expression of CD56, CD200, CD28, CD117, CD81 and CD19 and was observed in 88.5%, 77%, 29%, 37%, 23% and 17% cases respectively. Two aberrant antigens were noted in all cases. CD81 + cases had a relatively higher quantity of monoclonal-protein (> 1 g/dl, p < 0.05) and renal insufficiency (Cr > 2 mg/dl, p < 0.05) as compared to the CD81- cases. CD229 was expressed in all the cases, with a median MFI in PCs significantly higher than other hematopoietic elements. Hyperdiploid PCs (median DI-1.59, range, 1.16–2.6) were noted in 80% cases (n = 48), diploid/ near-hyperdiploid PCs in 8% (n = 5) cases and hypodiploidy in 3% (n = 1) cases. Bright CD56/CD200 and CD45- can identify abnormal PC in the majority of the cases. CD81 appears to correlate with disease burden and might be useful as a prognostic marker. CD229 is a reliable gating marker for plasma cells. Ploidy analysis may be incorporated in routine workup to guide in the identification of patients with poor prognosis.