OBJECTIVES:  In 2005, bortezomib received regulatory approval in Canada for the treatment of multiple myeloma (MM) patients who have relapsed following front-line therapy and are refractory to their most recent therapy.  Prior to this approval, treatment options for this patient group was very limited and included best supportive care (BSC).  The objective was to conduct an economic analysis of bortezomib versus BSC in relapsed and refractory MM patients.  METHODS:  The clinical evidence (survival and QOL) for the analysis was taken from the SUMMIT trial (NEJM 2003; 384:2609-2617), a Phase II trial of bortezomib in 202 relapsed and refractory MM patients.  These patients were heavily pre-treated with a median of six prior lines of therapy.  In order to properly represent such a refractory group of patients, the Progressive Disease subgroup of patients in SUMMIT were used to estimate how a BSC group would perform.  Utility score was indirectly obtained from mapping patient QOL (EORTC-QLQC30, MY24, FACIT-Fatigue, FACT/GOG-Ntx) onto dimensions in ED-5D.  Resource use from SUMMIT was used to estimate costs from the Ontario Ministry of Health perspective.  RESULTS:  Bortezomib produced a survival gain of 9.95 months (range 7.75 to 12.09 months), a QALY gain of 0.53 QALY, and an incremental cost of CAN$37,662 per patient.  The incremental cost-effectiveness ratio (ICER) was CAN$45,399 (range $37,380 to $58,288) per LY and incremental cost-utility ratio (ICUR) was CAN$70,852 (range $58,189 to $89,791) per QALY.  Sensitivity analyses did not produce wide changes in the ICER or ICUR.  CONCLUSIONS:  Bortezomib is a cost-effective option for this patient population that has limited available therapies.