A Multicenter Randomized Phase II Trial of Mapatumumab, a TRAIL-R1 Agonist Monoclonal Antibody, In Combination with Bortezomib In Patients with Relapsed/Refractory Multiple Myeloma (MM)

Abstract 5031

Mapatumumab, a fully human monoclonal antibody, targets and activates the TRAIL-R1 receptor. We conducted this randomized, controlled phase II trial to evaluate the efficacy and safety of mapatumumab in combination with bortezomib in subjects with relapsed/refractory MM. Response was evaluated using the Bladé criteria. Patients were required to have a measurable serum and/or urine M-protein and have failed 1 or 2 prior therapies for MM. Patients were excluded if they had received prior bortezomib. Patients were randomly assigned to Arm A, 1.3 mg/m² bortezomib (days 1, 4, 8, 11) every 21 days; Arm B10, bortezomib + 10 mg/kg mapatumumab (day 1) every 21 days; or Arm B20, bortezomib + 20 mg/kg mapatumumab (day 1) every 21 days. Cycles were repeated every 21 days for a maximum of 17 cycles (1 year), progressive disease or unacceptable toxicity. Subjects with complete response (CR) were treated for an additional 2 cycles after documentation of CR (not to exceed 17) and then followed. A total of 104 subjects from 4 countries were randomly assigned to the treatment arms. The addition of mapatumumab to bortezomib did not increase the response rate, progression-free survival (PFS) or duration of response compared to bortezomib alone. Adverse events were generally balanced across treatment groups; there was no evidence that mapatumumab exacerbated toxicities associated with bortezomib. As expected, the most common toxicities were hematological and peripheral neuropathies. The results do not support further evaluation of mapatumumab in combination with bortezomib in patients with advanced MM. Additional trials of mapatumumab in other indications are on-going.