Bortezomib plus dexamethasone for relapsed or treatment refractory multiple myeloma: the collaborative study at six institutes in Kyoto and Osaka.

We conducted a retrospective collaborative investigation of bortezomib (Bor) plus dexamethasone (Dex) therapy (BD Tx) for 88 relapsed or refractory (Rel/Ref) MM patients at six institutes. One cycle BD Tx comprised of Bor (1.3 mg/m²/day) on days 1, 4, 8 and 11, and Dex on days 1, 2, 4, 5, 8, 9, 11 and 12, every 21 days, and the mean number of BD Tx cycles was 3. The overall response rate was 66.9%, the median overall survival (OS) was 510 days, and the median progression-free survival (PFS) was 113 days. Attainment of partial response (PR) with the first course of BD Tx associated with the longer OS and PFS and late good responder, while no patient who did not achieve PR with the first cycle attained better than very good PR (VGPR) with the subsequent BD Tx. Patient age of less than 64 years old also associated with the longer OS and PFS. In addition, both an earlier disease stage and Dex dosage had a significant impact on OS, while the attainment of VGPR within 2 cycles had a significantly longer PFS. Earlier BD Tx courses may be predictive for the subsequent therapeutic pathway of Rel/Ref MM.