The genetic landscape of extramedullary plasmacytoma: a comparative analysis with extramedullary disease of multiple myeloma.

Extramedullary (or extraosseous) plasmacytoma (EMP) is a localized plasma cell neoplasm lacking apparent bone marrow involvement and other features of multiple myeloma (MM). The prognosis is usually favorable and progression to MM is infrequent. The genetic landscape of EMP remains largely unknown. Importantly, EMP must be distinguished from extramedullary disease of MM (EMD), which typically exhibits aggressive behavior. We performed a comprehensive molecular analysis of EMP (n=24) in comparison to EMD (n=24) using fluorescence in situ hybridization (FISH), copy number (CN) profiling, and targeted nextgeneration sequencing. Overall, EMP shared several genetic features with MM, but exhibited markedly lower complexity than EMD. EMP revealed a mean of 4.3 CN changes vs. 19.3 in EMD (p.