Preliminary Safety and Efficacy Results from an International Phase 3b Study for Expanded Access to Bortezomib in 624 Patients with Relapsed and/or Refractory Multiple Myeloma.
Authors: Mikhael Joseph R. , Belch Andrew , Prince Miles , Lucio Maria Nambo , Maiolino Angelo , Corso Alessandro , Petrucci Maria Teresa , Mieczyslaw Komarnicki , Stewart A. Keith 
Published: October 2019

Background: Bortezomib (VELCADE®) is a first-in-class, reversible proteasome inhibitor with activity in multiple myeloma (MM) and other malignancies. Bortezomib showed significant activity in previous phase 2 and 3 studies in patients (pts) with previously treated MM. This international multicenter open-label phase 3b study allowed expanded access to bortezomib therapy in pts with relapsed/refractory MM treated with ≥ 2 previous lines of therapy.

Methods: Pts with MM were eligible if they had received ≥ 2 prior lines of therapy and required treatment due to relapsed or progressive disease. Pts with grade ≥ 2 peripheral neuropathy (PN) were excluded. Pts received 1.3 mg/m2 IV bolus bortezomib on days 1, 4, 8, and 11 of each 3-week cycle for up to 8 cycles; dexamethasone (20 mg/d PO on the day of and day after bortezomib dose) could be added after cycle 2 for progressive disease or after cycle 4 for stable disease. Adverse events (AEs) were assessed beginning at the start of treatment and continuing until 30–42 days after treatment and were graded based on NCI-CTC version 2.0. Efficacy assessment was performed based on changes in disease burden as measured by monoclonal (M)-protein concentration in serum and urine every 2 cycles (6 weeks). Response was assessed using modified SWOG criteria: complete response (CR) was a 100% reduction in M-protein; very good partial response (VGPR), 75–99% reduction; partial response (PR), 50–74% reduction; minimal response (MR), 25–49% reduction; and stable disease, < 25% reduction. Increasing M-protein levels indicated progressive disease.

Results: 624 pts in 93 centers from 21 countries received at least 1 dose of treatment and were evaluable for safety (55.3% male; median age 62.7 years). 68% of pts received 3–11 lines of previous therapy. Karnofsky performance status was ≤70 in 25.6% of pts; 141 pts (22.6%) were ≥ 70 years of age. Pts completed a median of 5 cycles of therapy (range 0–13); 39.3% of pts completed all 8 planned cycles. Grade 3/4 treatment-emergent (related and unrelated) AEs were reported in 430 pts (68.9%), with thrombocytopenia (29.2%), neutropenia (13.3%), and anemia (11.7%) the most common hematologic AEs. Grade 3/4 PN was reported in 8.2% of pts. Overall, 165 pts (26.4%) discontinued therapy due to treatment-related AEs. Best responses among evaluable pts (n = 593) included 12.0% CR, 23.1% VGPR, 19.1% PR, and 16.5% MR, for an overall response rate of 70.7%. Median time to first response was 42 days (range 7–125), and median time to best response was 63 days (range 7–235).

Conclusions: Bortezomib 1.3 mg/m2 administered biweekly q3 weeks was well tolerated with manageable toxicities in pts with relapsed and/or refractory MM. Response rates with bortezomib were high, even in heavily pretreated pts, inducing > 25% CR/VGPR. This study confirms results from initial clinical trials in a broader population.