Features of extramedullary and extraosseous multiple myeloma: a report of 19 patients from a single center

Extramedullary (EM) localizations at diagnosis or during the course of multiple myeloma (MM) are rare. We conducted a large retrospective study to more accurately describe the clinical and laboratory features of this entity, and the outcome of these manifestations. The charts of 19 eligible patients out of 432 patients with MM were retrieved from the hematology department of the Institut Paoli-Calmettes Cancer Center. Median age was 61 (range: 39-79) with a female/male sex ratio of 8/11. Ten patients were found to have EM and extraosseous tumor at the time of MM diagnosis, and nine patients developed EM tumor during the course of the disease. Neither the stage of the disease, the LDH level, or the type of immunoglobulin (Ig) was found to be associated with the development of EM disease. Patients who developed EM tumor during the course of MM had a lower serum Ig and a higher monoclonal Bence-Jones proteinuria at the diagnosis of MM than patients who presented with EM tumor at diagnosis. Multiple sites were usually involved. Resistance to chemotherapy was frequent and response to thalidomide was poor. Eight out of the 19 patients responded to high-dose chemotherapy. The remaining 11 patients progressed while on therapy. With a median follow-up of 13 months (range: 2-65), six patients are alive, four patients are in partial remission and two patients in present progressive disease. In conclusion, EM tumors are a rare manifestation of MM, with a cumulative incidence of 4.6% of MM. Multiple sites are usually involved. The response to chemotherapy is very poor with a very low response rate to thalidomide. The prognosis is very poor, especially when the diagnosis of EM tumor is concurrent with the diagnosis of MM.