Extramedullary Myeloma Spread Triggered by Surgical Procedures: An Emerging Entity?

Abstract

Multiple myeloma (MM) is characterized by a proliferation of malignant plasma cells with a strong dependence on the bone marrow microenvironment. However, in patients with MM, the plasma cell proliferation can escape the microenvironment influences and result in extramedullary soft-tissue plasmacytomas (EMPs) which can constitute the most prominent feature of the disease. In fact, the reported incidence of EMPs in MM ranges from 7 to 18% at diagnosis and is as much as 20% at the time of relapse [1,2,3,4]. Soft-tissue plasmacytomas have two main origins: (1) direct growth from skeletal plasma cell tumors disrupting the cortical bone and (2) hematogenous spread [1]. It has been suggested that patients undergoing allogeneic transplantation, particularly those receiving reduced-intensity conditioning, may have a higher incidence of extramedullary disease (EMD) than those who receive an autologous stem-cell transplant. However, the incidence of EMD after allogeneic versus autologous stem-cell transplant has not been studied in comparable groups of patients. It has also been suggested that EMD is more frequent in patients exposed to novel agents. Nevertheless, a recent study showed that previous exposure to thalidomide or bortezomib was not associated with a higher risk of extramedullary relapse [3]. In addition, the study showed that up to 45% of patients with EMPs at diagnosis develop EMD at the time of relapse, and a multivariate regression analysis showed that the presence of EMD at diagnosis was the only predictor of extramedullary recurrence. The above features support the notion that characteristics inherent to the myeloma clone or host, rather than the treatment, are responsible for extramedullary spread in MM. As far as the development of EMD is concerned, local growth of soft-tissue masses arising from bone lesions is the most frequent mechanism, and second to this is the hematogenous spread that can involve any tissue or organ, the most frequent sites being the skin, liver, kidney, lymph nodes and central nervous system [1,2]. Positron emission tomography/computed tomography imaging may be very helpful in the search for EMD and these scans should be performed on all patients with suspicious of extramedullary involvement.