Efficacy and Safety of Once Weekly Bortezomib In Multiple Myeloma Patients

In a recent phase 3 trial, bortezomib–melphalan – prednisone–thalidomide followed by maintenance treatment with bortezomib–thalidomide (VMPT-VT) demonstrated superior efficacy compared with VMP. Peripheral neuropathy (PN) was the most important dose limiting toxicity. To decrease neurologic toxicities, the protocol was amended and patients in both arms received once-weekly instead of the initial twice-weekly bortezomib infusions. This post-hoc analysis assessed the impact of bortezomib dose-modification schedule on clinical outcomes and safety.

Patients (N=511) older than 65 years were randomized to receive nine 6-week cycles of VMPT-VT (N=254; induction:V 1.3 mg/m², d 1, 4, 8, 11, 22, 25, 29, 32, cycles 1–4, d 1, 8, 22, 29, cycles 5–9; M 9 mg/m² d 1–4, P 60 mg/m², d 1–4, T 50 mg d 1–42; maintenance: V 1.3 mg/m² every 14 days and T 50 mg/day) or VMP (N=257) alone. In March 2007, the protocol was amended: both VMPT-VT and VMP induction schedules were changed to nine 5-week cycles and bortezomib schedule was modified to weekly administration (1.3 mg/m² d 1,8,15,22, all cycles). Patients receiving VMPT-VT and VMP were pooled together and stratified according to the once-weekly or twice-weekly infusion modality; analyses were also conducted for patients receiving VMP only, to eliminate the influence of thalidomide and of maintenance on efficacy and safety.

Patients were evaluated in intention-to-treat: 372 patients received once-weekly and 139 twice-weekly bortezomib infusion. Patient characteristics were similar in the two groups, median age was 71 years. The efficacy data did not appear to be affected by the bortezomib schedule. Overall response rates were 85% with once weekly and 86% with twice- weekly schedule (P = .78), including CR rates of 30% and 35% (P = .27).Three-year PFS was 50% in the once-weekly and 47% in the twice-weekly group (P = 1.00), and 3-year OS was 88% and 89%, respectively (P = .54). Similar outcome was seen in the analyses restricted to VMP patients: CR rates were 23% with once-weekly and 27% with twice-weekly schedule (P = .54), 3-years PFS was 46% in once-weekly and 39% (P = .86) in twice-weekly group and 3-years OS was 87% and 89% (P = .47), respectively. The incidence of grade 3/4 hematologic toxicity was similar in the two groups (44% vs 45%, P = .83), but severe thrombocytopenia was slightly less common in the once-weekly patients (19% vs 26%, P = .08).The incidence of non-hematologic grade 3/4 adverse events was significantly reduced in the once-weekly: 35% vs 51% (P = .003). Grade 3/4 gastrointestinal events (6% vs 11%, P = .08), severe systemic events (4% vs 7%, P = .09) and grade 3/4 dermatologic events (2% vs 7%, P = .006) were less frequent in patients receiving once-weekly bortezomib. There was a significantly reduced overall incidence of grade 3/4 PN (8% vs 28%, P < .001) in the once-weekly group. The median time to onset of grade 3/4 sensory PN was 4.3 months in the once-weekly group and 3.2 months in the twice-weekly group (P = .10). The cumulative incidence of sensory PN appeared to plateau after 12 months of therapy in both groups. Rates of discontinuations (5% versus 15%) and dose reductions (15% versus 41%) due to PN were also significantly lower in the once-weekly group (P < .001). These results were reflected in analysis restricted to VMP patients, in which the incidence of grade 3/4 PN (7% vs 29%, P < .001), the discontinuation rate (4% vs 16%, P = 0.002), and the dose reductions rate (15% vs 41% P < 0.001) were significantly lower in once-weekly group. Despite the cumulative planned dose being lower in the once-weekly group (46.8 vs 67.6 mg/m²), the delivered cumulative dose of bortezomib was similar in the two groups (39.4 mg/m² vs 40.1 mg/m²). No association of PN with age or other baseline characteristics was outlined. The only significant factor influencing the incidence of PN was the reduction of bortezomib infusion from twice- to once-weekly (p<0.001). Low dose thalidomide did not affect grade 3/4 PN rate (p=0.16).

These results demonstrate that 1. both once-weekly and twice-weekly schedules in combination with MP ± thalidomide are highly effective in patients ≥ 65 years; 2. once-weekly schedule significantly reduced the incidence of PN and decreased the rate of discontinuation, resulting in similar cumulative bortezomib doses in the two groups; 3. the improvement in the safety profile was not associated with any reduction in the efficacy.

Bringhen:Celgene: Honoraria; Janssen Cilag: Honoraria. Leoni:Celgene: Honoraria; Janssen Cilag: Honoraria. Patriarca:Celgene: Honoraria; Janssen Cilag: Honoraria; Roche: Honoraria; Merck: Membership on an entity's Board of Directors or advisory committees. Guglielmelli:Celgene: Honoraria; Janssen Cilag: Honoraria. Elice:Celgene: Honoraria; Novatis: Honoraria. Boccadoro:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen-Cilag: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Palumbo:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen-Cilag: Honoraria, Membership on an entity's Board of Directors or advisory committees.