Clinicopathological features of extramedullary recurrence/relapse of multiple myeloma.

Extramedullary relapses of multiple myeloma (MM) during the course of disease are rare. We report a series of six patients with primary intramedullary MM that were treated with immunomodulatory therapy and/or stem cell transplant, and that later developed extramedullary relapses at various body sites. These six cases represent 3.9% of the 156 patients treated for MM at our institution over a 9-yr period (1999-2007). Five (83.3%) of the six cases showed immature/high-grade histology in the extramedullary relapses as compared with their antecedent MM. The neural cell adhesion molecule, CD56, was immunohistochemically demonstrable in 75% (three of four) of the original myelomas tested, but was absent in 83.3% (five of six) of their extramedullary relapses. The disease typically behaved aggressively and was rapidly fatal in all six patients even when therapy was administered. The median time of progression to extramedullary relapse was 29 months (range 9-64 months), and the median survival after diagnosis of the relapses was only 38 d (range 1-106 d). Our case series shows that extramedullary relapse of MM is characterized by high-grade histology, loss of CD56 expression, frequent resistance to current therapeutic regimens, aggressive biological behavior, and very short survival.