Plasmacytoma in patients with multiple myeloma: morphology and immunohistochemistry
Abstract Background. To study the histological structure and immunohistochemical (IHC) parameters of the plasmacytoma tumor substrate in patients with MM. Methods. The study included 21 patients (10 men/11 women) aged 23 to 73 years old with a newly diagnosed MM complicated by plasmacytoma. Bone plasmacytoma was diagnosed in 14 patients, and extramedullary plasmacytoma was diagnosed in 7 patients. Plasmacytoma tissue specimens were examined using a LEICA DM4000B microscope. Anti-CD56, CD166, CXCR4, Ki-67, c-MYC antibody panels were used for the IHC study of plasmacytoma biopsy. Results. When comparing the morphology of bone and extramedullary plasmacytoma, no significant differences were revealed, however, when the substrate of the extramedullary plasmacytoma was compared to the bone plasmacytoma substrate it was more often represented by tumor cells with immature morphology (57.1% vs. 28.6%). We founded a significant difference in the expression of CD166 in bone and extramedullary plasmacytoma. It was shown that the mean values of the CD166 expression in bone plasmacytoma cells were significantly higher (p = 0.033) and amounted to 36.29 ± 7.61% versus 9.57 ± 8.46% in extramedullary plasmacytoma cells. We noticed that in the cells of the extramedullary plasmacytoma, there were higher values in the Ki-67 index than observed in comparison to the cells of the bone plasmacytoma independent of the cells’morphology. Conclusion. The mechanisms involved in the dissemination of tumor plasma cells are currently unexplored. Our study revealed significant differences in the IHC parameters of the tumor substrate from extramedullary and bone plasmacytoma. Thus, the expression of the CD166 in extramedullary plasmacytoma cells is almost 4 times lower than that in bone plasmacytoma cells, which may indicate the involvement of CD166 in the mechanisms of bone destruction. A high proliferative activity of extramedullary plasmacytoma cells was shown when compared to bone plasmacytoma cells.