Extramedullary multiple myeloma.

Abstract Extramedullary disease (EMD), defined as a clonal plasmacytic infiltrate at anatomic sites distant from the bone marrow or adjacent soft tissue in a patient with underlying multiple myeloma, is present in a significant percentage of patients with multiple myeloma at some point during the course of their disease. The exact prevalence of EMD, however, has not been reproducibly described, with some series citing EMD in 6% of patients with myeloma, and others up to 20%. EMD is therefore an uncommon, but by no means rare, manifestation of multiple myeloma. Further observational series have suggested that EMD is a highly aggressive disease entity, with clinical behavior distinct from marrow-restricted myeloma. This article summarizes the current research on EMD and examines the opportunity for further research into the pathogenic, immunologic, cytogenetic, clinical, therapeutic and prognostic features of this hitherto poorly understood disease entity.