Bortezomib maintenance therapy in transplant-ineligible myeloma patients who plateaued after bortezomib-based induction therapy: a multicenter phase II clinical trial.

In the era of novel therapeutic agents for multiple myeloma (MM), both the significance of achieving the plateau phase and the efficacy of subsequent maintenance therapy remain unclear. In the present study, we evaluated the efficacy and safety of bortezomib maintenance therapy (biweekly for 1 year) in transplant-ineligible MM patients who plateaued after bortezomib-based induction therapy. Of 36 evaluable patients, the overall response rate during induction therapy was 61%, with a stringent complete response in 6%, a complete response in 6%, a very good partial response in 17%, and a partial response in 33%. Twenty patients achieved the plateau phase and subsequently received bortezomib maintenance therapy. Median progression-free survival from the induction and maintenance therapies was 13.8 months (95% confidence interval, 11.4-23.7 months) and 10.7 months (95% confidence interval, 3.7-10.7 months), respectively. During maintenance therapy, there were no cases with grade ≥ 2 peripheral neuropathy, nor was there any improvement in the quality of the response. In conclusion, although maintenance therapy with biweekly bortezomib for up to 1 year was feasible, plateau-oriented bortezomib induction therapy followed by bortezomib maintenance therapy was not adequate in newly diagnosed transplant-ineligible MM patients.