Clinical and Biological Characteristics of Medullary and Extramedullary Plasma Cell Dyscrasias

Simple Summary Extramedullary disease can occur either in multiple myeloma at the initial diagnosis or relapse or as primary extramedullary plasmocytoma/solitary osseous plasmocytoma. The exact molecular mechanisms underlying extramedullary spread of clonal plasma cells are not fully understood. The aim of our study was to assess further insights into clinical and biological characteristics of different types of extramedullary plasma cell disorders. We show that expression profiles of molecules involved in homing and cytogenetic abnormalities differ between various types of plasma cell dyscrasias, indicating the contrasting biology of these diseases. Background: Extramedullary plasma cell (PC) disorders may occur as extramedullary disease in multiple myeloma (MM-EMD) or as primary extramedullary plasmocytoma (pEMP)/solitary osseous plasmocytoma (SOP). In this study, we aimed to obtain insights into the molecular mechanisms of extramedullary spread of clonal PC. Methods: Clinical and biological characteristics of 87 patients with MM-EMD (n = 49), pEMP/SOP (n = 20) and classical MM (n = 18) were analyzed by using immunohistochemistry (CXCR4, CD31, CD44 and CD81 staining) and cytoplasmic immunoglobulin staining combined with fluorescence in situ hybridization (cIg-FISH). Results: High expression of CD44, a cell-surface glycoprotein involved in cell-cell interactions, was significantly enriched in MM-EMD (90%) vs. pEMP/SOP (27%) or classical MM (33%) (p < 0.001). In addition, 1q21 amplification by clonal PC occurred at a similar frequency of MM-EMD (33%), pEMP/SOP (57%) and classical MM (44%). Conversely, del(17p13), t(4;14) and t(14;16) were completely absent in pEMP/SOP. Besides this, 1q21 amplification was identified in 64% of not paraskeletal samples from MM-EMD or pEMP compared to 9% of SOP or paraskeletal MM-EMD/pEMP and 44% of classical MM samples, respectively (p = 0.02). Conclusion: Expression of molecules involved in homing and cytogenetic aberrations differ between MM with or without EMD and pEMP/SOP.