Extended follow-up of a Phase II trial in relapsed, refractory multiple myeloma: Final time-to-event results from the SUMMIT trial

BACKGROUND. Bortezomib, a first-in-class proteasome inhibitor, has shown clinical activity in relapsed, refractory multiple myeloma in a pivotal Phase II trial, SUMMIT. METHODS. Patients received bortezomib 1.3 mg/m² on Days 1, 4, 8, and 11 followed by a 10-day rest period for up to 8 cycles. Dexamethasone 20 mg on the day of and the day after bortezomib was permitted for suboptimal response. Extended treatment beyond 8 cycles was offered to patients whose physicians felt they would benefit from additional therapy. Follow-up was conducted in all patients for a median of 23 months, an additional 13 months from the original report. RESULTS. Of 202 patients enrolled in SUMMIT, 193 were evaluable for response. Seven (4%) patients achieved a complete response, 12 (6%) achieved a nearly complete response, 34 (18%) achieved a partial response, and 14 (7%) had a minimal response while on bortezomib. The updated median duration of response to bortezomib alone was 12.7 months. The median overall time to progression for all SUMMIT patients was 7 months. For responding patients, the median time to progression was 13.9 months, whereas for those with progressive disease (PD) or who were not evaluable, the median time to progression was 1.3 months. The median overall survival (OS) for all SUMMIT patients was 17.0 months. Whereas the median OS for patients with PD or who were not evaluable was 8 months, the median OS for responding patients was not reached at 23 months of follow-up. CONCLUSIONS. These data demonstrate that treatment with bortezomib results in meaningful long-term benefit for patients with relapsed and refractory myeloma.