A prospective, international phase 2 study of bortezomib retreatment in patients with relapsed multiple myeloma.

Multiple myeloma (MM) typically follows a relapsing course with many patients requiring multiple therapies. This single-arm phase 2 study prospectively evaluated the efficacy and safety of bortezomib retreatment in MM patients who had relapsed after achieving at least a partial response (≥ PR) to prior bortezomib-based therapy. Patients aged ≥ 18 years, with measurable, secretory MM, who relapsed ≥ 6 months after prior bortezomib treatment were eligible. Patients received up to eight cycles of bortezomib (± dexamethasone). The primary endpoint was best confirmed response at retreatment; secondary endpoints included duration of response (DOR), time to progression (TTP), and safety. Adverse events (AEs) were graded by National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. A total of 130 patients (median of two prior lines of therapy) were enrolled and received retreatment. At retreatment, 28% and 72% of patients received bortezomib and bortezomib-dexamethasone, respectively. Overall response rate was 40%. In patients who achieved ≥ PR, median DOR and TTP were 6.5 and 8.4 months, respectively. Thrombocytopenia was the most common grade ≥ 3 AE (35%). Forty percent of patients experienced neuropathy events, which improved and resolved in a median of 1.5 and 8.9 months, respectively. In conclusion, bortezomib retreatment was effective and tolerable in relapsed MM patients, with no evidence of cumulative toxicities.