Unusual Discordant Responses in Two Multiple Myeloma Patients during Bortezomib Treatment

BACKGROUND: Cases of discordant responses in multiple myeloma (MM) patients after thalidomide therapy have been sometimes reported, in which extramedullary masses progress or present de novo with a simultaneous serum monoclonal protein reduction. PATIENTS AND METHODS: We hereby report, for the first time, on two cases of MM patients with extramedullary myeloma localizations that developed during Velcade (bortezomib, PS341) treatment with a concomitant serum monoclonal protein reduction. RESULTS: We observed in both patients a very good response in the serum monoclonal protein level, while extramedullary lesions appeared in the central nervous system and subcutaneously. CONCLUSIONS: We discuss pharmacokinetics of bortezomib and physiopathology of this unusual event and review the literature.