Increased Circulating Plasma Cells Predicts Poor Overall Survival in Symptomatic Plasma Cell Myeloma Patients

Backgrounds

Flow cytometry can rapidly determine immunophenotypes of neoplastic plasma cells (PCs) and quantify PCs in patients with plasma cell myeloma. Flow cytometric immunophenotyping and quantification of neoplastic plasma cells is sensitive and reliable tool for diagnosis and disease monitoring in patients with monoclonal gammopathy. Circulating PCs (cPCs) in peripheral blood (PB) after autologous hematopoietic stem cell transplantation is a marker of high-risk disease in patients with plasma cell myeloma. We assessed the utility of quantification of cPCs using flow cytometry for risk stratification in newly diagnosed plasma cell myeloma patients in the era of novel agents.

 

Methods

PB and bone marrow (BM) aspirates of 85 newly diagnosed patients with symptomatic plasma cell myeloma from August 2013 to July 2014 were analyzed by five-color flow cytometry using monoclonal antibodies against CD45, CD19, CD56, CD38, and CD138. The gating strategy employed first used the expression of CD38 and CD138 to identify plasma cells among 100,000 to 200,000 events. cPCs in PB was determined according to the patient's specific immunophenotype of neoplastic PCs in BM.

 

Results

The median age of the patient population was 68 years (45~87) and 58% were female. Median follow-up duration was 19.2 months. Six out of 85 patients (7%) did not show cPCs. Among 79 patient (93%) who had detectable cPCs, the median cPCs was 0.09% (0.006~3.612%). Patients without cPCs or cPCs under 0.05% were assigned to low cPCs group (n=32, 38%) and others to high cPCs group (n=53, 62%) according to receiver operating characteristics analysis. High cPCs group showed higher level of BM neoplastic PCs detected by both methodologys of morphology and flow cytometry (P=0.002, 0.033, respectively), higher BM cellularity (P=0.011), higher serum M protein level (P=0.013), lower hemoglobin (P=0.008), and lower platelet level (P=0.034) than low cPCs group. High cPCs group was associated with adverse cytogenetics such as t(4;14) and monosomy 13 (P=0.008), and CD45 negative immunophenotype (P=0.007). In survival analysis, high cPCs presented shorter overall survival (OS) than low cPCs group (P=0.013) (Fig. 1). It was independent with patient age and cytogenetic risks (P=0.011).

Conclusion

By flow cytometry cPCs was detected in most symptomatic plasma cell myeloma patients. Increased cPCs ≥0.05% among PB leukocytes could be an independent prognostic factor showing adverse effect in overall survival in symptomatic plasma cell myeloma patients.

Figure 1. Kaplan-Meier survival curve of patients with plasma cell myeloma who showed 0.05% or more circulating plasma cells in peripheral blood and patients with circulating plasma cells less than 0.05%.