Background: There are few data on the incidence and prognosis of extramedullary (EM) multiple myeloma (MM). There are concerns about a possible increase of EM relapses with the expanding use of high-dose therapy (HDT) and biological agents.
Patients and methods: The incidence of EM disease, its relationship with prior exposure to HDT or novel agents, and its prognostic impact were analyzed in 1003 MM patients. Based on the different therapies available, three periods were considered: 1971-1993, conventional-dose chemotherapy; 1994-1999, HDT for younger patients; and 2000-2007, introduction of novel agents.
Results: Overall, 13% of patients had EM disease, 7% at diagnosis and 6% later. In the 2000-2007 period, there was a significant increase of EM involvement, at diagnosis (P = 0.02) and during follow-up (P = 0.03). The risk of EM spread was not significantly increased after HDT [hazard ratio (HR 0.6)], bortezomib (HR 1.62), or thalidomide/lenalidomide (HR 1.07). EM disease was associated with shorter overall (HR 3.26, P < 0.0001) and progression-free (HR 1.46, P = 0.04) survival.
Conclusions: The incidence of EM disease has increased, probably due to the availability of more sensitive imaging techniques and the prolongation of patients' survival. HDT or novel agents seem not to increase the risk of EM disease. EM involvement confers a poor prognosis.