Purpose: The combination of oral weekly cyclophosphamide and alternate day prednisone is a convenient regimen for relapsed/refractory multiple myeloma (MM), and we sought to improve its efficacy by adding bortezomib, a proteasome inhibitor with proven antimyeloma activity.
Patients and methods: We conducted a phase I-II trial evaluating six dose levels to define the maximum tolerated dose (MTD) of this combination in relapsed/refractory MM. An additional 10 patients were evaluated at the highest dose level reached.
Results: Thirty-seven patients were treated on this study. The MTD was not defined. Both of the highest dose levels of bortezomib tested (1.3 mg/m(2) on days 1, 4, 8, and 11 and 1.5 mg/m(2) on days 1, 8, and 15, each on a 28-day cycle) could be safely given with cyclophosphamide 300 mg/m(2) per week and prednisone. At these dose levels, the overall response rate was 95% (complete responses [CR] plus partial response plus minimal response), with CR observed in more than 50% of patients. The weekly bortezomib regimen resulted in fewer instances of grade 3 thrombocytopenia and grade 1 to 2 peripheral neuropathy; the 1-year progression-free and overall survival probabilities with this dose level were 83% (95% CI, 73% to 96%) and 100%, respectively.
Conclusion: Weekly bortezomib 1.5 mg/m(2) plus oral cyclophosphamide and prednisone produces an unprecedented response rate and encouraging 1-year survival in relapsed/refractory patients with MM. Further evaluation of this promising regimen is warranted both in relapsed and newly diagnosed disease.