Incidence and Clinical Features of Extramedullary Multiple Myeloma in Patients Who Underwent Stem Cell Transplantation

Background: Extramedullary disease (EMD), strictly defined as an infiltrate of clonal plasma cells at an anatomic site distant from the bone marrow or adjacent soft tissue in a patient with underlying multiple myeloma, is an uncommon manifestation of multiple myeloma. Comparatively little is known about this disease entity, with no large case series published in the last decade. Patients and Methods: 663 consecutive patients with multiple myeloma who underwent autologous or allogeneic stem cell transplantation at a single, large, academic medical center in the United States from January 2005 to December 2011 were assessed for the presence or absence of EMD, as well as baseline demographic and biochemical characteristics, treatment regimens, and response to therapy. Results: A cohort of 55 patients with biopsy-proven EMD was identified, comprising 8.3% of the total study population. Among the patients with EMD, 13 (23.6%) were found to have EMD at the time of initial presentation, while the remainder developed EMD during the course of their illness. Patients with EMD received a median of 5 different treatment regimens during the course of their illness, most commonly with combinations of dexamethasone, thalidomide, lenalidomide, and bortezomib, as well as autologous hemotopoietic stem cell transplantation. Patients had received a median of 3 lines of therapy prior to experiencing an extramedullary relapse. Patients with EMD had markedly elevated maximum serum LDH levels (median 613.5 units/L) and low minimum hemoglobin levels (median 7.8 g/dL). Common cytogenetic abnormalities included deletion 13q, deletion 11q, t(11;14), and deletion 17p. Available immunohistochemical data suggest that EMD specimens had frequent expression of CXCR4, CD44, and CD56. The median overall survival data of these patients was 3.2 years (range, 0.9-9.5) and the median time from diagnosis of EMD to death was 0.5 years (range, 0.002-3.2). Conclusions: This report describes a large series of multiple myeloma patients with EMD who were treated in the era of stem cell transplant at a single academic medical center. Further studies to examine the molecular characteristics of extramedullary multiple myeloma are necessary to better define this entity and characterize therapeutic options that can prolong survival in this otherwise very vulnerable population.