DOES CHARACTERISTIC PHENOTYPE FOR PLASMA CELL LEUKAEMIA EXIST?

ABSSUB-4953

Background: Plasma cell leukaemia (PCL) is characterized by a presence of circulating plasma cells (PCs) in peripheral blood. Primary PCL (pPCL) occurs in patients with no evidence of multiple myeloma (MM) while secondary PCL (sPCL) is end-stage of relapsed and/or refractory MM. Detection of circulating PCs by flow cytometry is important for diagnosis determination and for discrimination of PCL from reactive plasmacytosis as well. Identification of phenotype profile characteristic for PCL could help in early treatment intervention.

Aims: Analyses of pPCL and sPCL to identify phenotype profile in comparison with MM.

Methods: Total of 86 patients was analysed: 12 patients with pPCL, 10 patients with sPCL and 64 newly diagnosed MM patients. Whole peripheral blood (PB) and/or bone marrow (BM) CD38⁺CD138⁺ PCs were analysed. Expression of surface antigens (CD19, CD20, CD27, CD28, CD44, CD56, and CD117) together with intracellular nestin was studied by flow cytometry. PCs were considered positive for given marker when its expression exceeds 20 %.

Results: There were found similar relative number of PCs in peripheral blood of pPCL (26.7 %) and sPCL (26.8 %), on the other hand, infiltration of bone marrow was the highest in sPCL (55.6 %) when compared to pPCL (39.2 %) and MM (5.8 %). No presence of CD19⁺ and/or CD20⁺ PCs was found in sPCL, but slightly increased number of positive cases was found in pPCL (16.7 % for CD19 and/or CD20 in PB; 18.2 % for CD19 and 27.3 % for CD20 in BM) when compared to MM (4.7 % for CD19 and 11.7% for CD20 in BM). Number of CD56⁺ positive cases was higher in BM of MM (87.5 %) then in pPCL (54.5 %) and sPCL (66.7 %), similar expression was found in PB (58.3 % for pPCL and 50.0 % for sPCL). Number of CD27 positive cases was the highest in BM of MM (MM 51.6 %; pPCL 9.1 %; sPCL 28.6 %); the same positivity of CD27 was found in PB of both PCLs (25.0 %). No big differences were detected in expression of CD28 in BM (30.0 % in pPCL, 42.9 % in sPCL and 22.6 % in MM) and /or PB (16.7 % in pPCL vs. 28.6 % in sPCL). Surprisingly both PCLs expressed CD44 in 100% of BM samples, while MM in 70.7 %; PB expression was lower in pPCL (85.7 %) then in sPCL (100.0 %). CD117 was mostly expressed in BM of sPCL (50.0 %) and MM (43.5 %) when compared to pPCL (10.0%), similar expression were found in PB of both PCLs (8.3 % in pPCL vs. 14.3 % in sPCL). Nestin, a marker of stem cell, was highly expressed in sPCL (80.0 %) and pPCL (75.0 %), but decreased in MM (36.1 %); PB expression in PCLs was not so different (57.1 % in pPCL vs. 66.7 % in sPCL).

Summary/Conclusion: Phenotype profile of pPCL and sPCL did not differ so much in peripheral blood and/or bone marrow, except for a disappearance of CD19 and CD20 in sPCL and decrease of CD117 in pPCL. Lower expression of CD56, CD27 and overexpression of CD44 with nestin was characteristic for both PCLs when compared to MM.

Supported by IGA NT12425 grant.

Keywords: Flow cytometry, Leukemia, Phenotype, Plasma cells

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