Extramedullary disease in multiple myeloma at diagnosis and over the course of the disease

Extramedullary disease (EMD) is an aggressive manifestation of multiple myeloma (MM) and is categorized into two distinct types: extramedullary-bone-related (EM-B) and extramedullary-extraosseous (EM-E). We aimed to investigate differences in the characteristics of disease and outcomes between these two types. This single-center, retrospective study included 132 patients with EMD who were diagnosed with MM between January 2010 and January 2020. Patients were divided into EM-B (n = 93) and EM-E (n = 39), and clinicopathological features and survival outcomes were analyzed. EMD was observed in 98 (74.2%) patients at initial diagnosis and in 34 (25.8%) during a relapse. EM-E was significantly associated with ≥ 2 involved sites, high bone marrow plasma cell percentage, high LDH and beta-2 microglobulin levels, anemia, and high-risk fluorescence in situ hybridization abnormalities compared to EM-B. Patients with EM-E had significantly shorter progression-free survival and overall survival than those with EM-B. Anemia, hypercalcemia, high LDH, EMD at relapse, ≥ 2 involved sites, and not receiving autologous stem cell transplantation were independent poor risk factors for survival. In conclusion, EMD is a heterogeneous entity, and this study demonstrated that patients with EM-E presented with different clinicopathological characteristics and had worse survival compared to those with EM-B.