Phase II PETHEMA trial of alternating bortezomib and dexamethasone as induction regimen before autologous stem-cell transplantation in younger patients with multiple myeloma: efficacy and clinical implications of tumor response kinetics.

PURPOSE: This is the first study in which bortezomib and dexamethasone were administered on an alternating basis as up-front therapy in multiple myeloma (MM). We investigated the efficacy and kinetics of response to each drug and safety. PATIENTS AND METHODS: Patients with newly diagnosed MM who were less than 66 years old were treated with bortezomib at 1.3 mg/m2 on days 1, 4, 8, and 11 (cycles 1, 3, and 5) and dexamethasone 40 mg orally on days 1 through 4, 9 to 12, and 17 to 20 (cycles 2, 4, and 6), followed by autologous stem-cell transplantation (ASCT). Responses were evaluated by modified European Bone Marrow Transplantation criteria. Random effects models were used to analyze the tumor response kinetics.
RESULTS: Forty patients were enrolled. Partial response (PR) or greater was 65% (12.5% complete response [CR], 10% very good PR [VGPR], and 42.5% PR) plus 17.5% minor response. Time to response was rapid, with 82% serum M-protein reduction achieved within the first two cycles. The M-protein decrease was similar with dexamethasone and with bortezomib (P = .48). Chromosome 13 deletion, t(4;14), and t(14;16) did not have a negative impact on response. Toxicity was low, with no grade 3 to 4 peripheral neuropathy and no grade 2 to 4 thrombocytopenia. The response rate after ASCT was 88%, with 33% CR (negative immunofixation) plus 22% VGPR.
CONCLUSION: Bortezomib alternating with dexamethasone is a highly effective induction regimen with low toxicity. The kinetic study has shown a high degree of heterogeneity in response and rapid effect from both agents, supporting the use of a short induction regimen before ASCT in MM.