Detection of Circulating Plasma Cells in Multiple Myeloma with Extramedullary Plasmacytoma

Objective: To detect the circulating plasma cells (cPCs) in patients of multiple myeloma (MM) with or withoutextramedullary plasmacytoma (EMP).

Methods: The 21 patients of MM samples were collected from April 2014 to April 2015. There were 12 males, 9 females, with a median age of 60 (49 to 76 years old). Peripheral blood and bone marrow were examined before treatment or after EMP. Multi parameter flow cytometry (MFC) was used to analyze abnormal plasma cells (tumor cells) in samples of bone marrow and CD138 MACS positive sorting peripheral blood. The antibodies used in the flow cytometry were CD38-APC, CD138-PE, CD81-PE-Cy7, CD45-PacBlue, CD19-Percp-Cy5.5, CD56-mCherry-PE-ef610, CD117-AmCyan, CD16, Zombie-APC-Cy7.

Results: In these 21 patients, he ratio of sex is 1.33:1, the median age is 60 (49-76). The immunoglobin type is as follows: IgG κ 7 cases, IgG λ 5 cases, IgG 2 cases, IgA κ 3 cases, IgA λ 2 cases, λ light chain 1 cases. The morphology of bone marrow aspiration showed more than 15% plasma cells and abnormal plasma cells can be seen in bone marrow in cytometry. 9 of 21 patients diagnosed MM with EMP, 2 of them find EMP when initial diagnosis and 7 of them find EMP in the course of disease (6 months to 8 years). The sites of the EMP included head, jaw, chest wall, side of the rib, the soft tissue of the sacral region and the vertebral body and all patients had bone involvement. In 17 patients with complete clinical data, bone marrow and peripheral blood specimens, the cPCs negative rate was 87.5%(7/8) in EMP negative patients, while the cPCs positive rate was 66.7% (6/9) in EMP positive patients, the difference among groups was statistically significant (chi square values: 5.13, p = 0.024).

Conclusion: MFC has been widely used in diagnosis and minimal residual disease surveillance of MM, here we established the detection method of cPCs in MM patients, and it is valuable for clinical diagnosis and prognosis judgment.