Incidence of Centrosome Amplification in Multiple Myeloma.

Abstract 2827

Poster Board II-803

Centrosome amplification (CA) has been previously detected in hematological malignancies including multiple myeloma (MM) and is usually associated with disease progression. CA leads to the formation of multipolar mitotic spindles that may lead to chromosome segregation errors and genomic instability. In this pilot study, we have evaluated the occurrence of CA in two populations of B-lineage cells including B-lymphocytes and plasma cells (PCs) of MM patients. We have analyzed possible associations of CA with established prognostic factors including the most common chromosomal abnormalities in malignant PCs.

Immunofluorescence labeling was used for the evaluation of centrosome amplification (CA) in B-cells (CD19+) and PCs (CD138+) of MM patients. The centrin (centrosome protein) copy numbers were used to define three cellular subpopulations: (1) no centrin signal (Non-CS), (2) 1-4 centrin signals (1-4CS) or (3) more than 4 signals of centrin (CA). Samples with ≥11% of B-cells or ≥10% of PCs with >4 fluorescence signals of centrin were considered CA positive. A total of 70 patients were evaluated for CA in PCs and/or B-cells, including 18 patients who had analysis of both cell types. The patient population characteristics were as follows: males/females 34/36, median age of 65 years (range, 40-84 years). Most patients had advanced stage of MM (DS II/III n = 48; ISS II/III; n = 21). Peripheral blood samples from 20 healthy donors were used as controls and for the estimation of CA positivity threshold for B-cells (Mean + 3SD).

There was a statistically significant difference between the percentage of B-cells subpopulations with centrosome amplification in MM patients and that in healthy donors ([Mean ± SD] 9.9 ± 7.9% versus 3.2 ± 2.5%; P<0.0001). The frequency of MM cases positive for CA was 34% (17/50) and 37% (14/38) based the analysis of PC samples and B-cell samples, respectively. Overall, 22% (4/18) MM patients were double-positive. No significant correlation was detected between B-cells and PCs (r=0.387; P=0.113) obtained from patients with both available samples. No significant associations were identified between CA status and the following common cytogenetic abnormalities in PCs: del(13)(q14) (p= 1.000); del(17)(p13) (p=0.132); gain(1)(q21) (p= 1.000), hyperdiploidy (p= 1.000).

In summary, we have confirmed the presence of centrosome amplification in B-cells of MM patients. Immunofluorescence staining is a sensitive method for the detection of abnormal subpopulations of B-cells that probably represent a reservoir of clonogenic cells in MM.

This study was supported by grants NR 8945-4/2006, MSM 0021622434, MZ LC 06027 and IGA NR 9317 from the Departments of Education and Health of the Czech Republic.