Final Overall Survival Results of a Randomized Trial Comparing Bortezomib Plus Pegylated Liposomal Doxorubicin with Bortezomib Alone in Subjects with Relapsed or Refractory Multiple Myeloma

Introduction

Previous results of an open-label, randomized, controlled, multicenter phase III study (DOXIL-MMY-3001) demonstrated that bortezomib+pegylated liposomal doxorubicin (PLD) was superior to bortezomib monotherapy in treating subjects with relapsed or refractory multiple myeloma (MM) whose disease had failed one or more lines of prior therapy. The risk of developing disease progression was significantly reduced by 45% with bortezomib+PLD (median time to progression (TTP) with bortezomib+PLD: 9.3 months, bortezomib: 6.5 months; HR=1.82, 95% confidence interval (CI) [1.41, 2.35]; p=0.000004). In the interim analysis, the 15-month overall survival (OS) rate for bortezomib+PLD was 76% (95% CI [70%, 83%]) compared with 65% (95% CI [58%, 73%]) for bortezomib alone (p=0.03)(Orlowski et al JCO 25: 3892-3901, 2007). A protocol-defined analysis of the final survival data of this study is provided here.

Methods

Subjects with confirmed MM, ECOG status 0 to 1, platelets ≥75,000/mm³, hemoglobin ≥8.0 g/dL, absolute neutrophils ≥1,000/mm³, and creatinine clearance ≥30 mL/min were randomized to bortezomib (bortezomib 1.3 mg/m², intravenous, days 1, 4, 8, and 11 of an every 21-day cycle), or bortezomib+PLD (same bortezomib+PLD 30 mg/m² intravenous on day 4). Randomization was stratified according to serum β₂-microglobulin levels (≤2.5, >2.5 and ≤5.5, or >5.5 mg/L) and response to prior treatment (response followed by progression, or primary refractory). The primary endpoint was TTP; secondary efficacy endpoints included overall survival, progression-free survival (PFS) and overall response rate (complete response [CR] + partial response [PR]).

Results

A total of 646 subjects (bortezomib+PLD: 324; bortezomib: 322) were randomized between December 2004 and March 2006. In the pre-planned interim analysis, the study met its primary and other secondary end points. The study continued for long-term survival follow-up. At the clinical cutoff of 16 May, 2014, for the final survival analysis with a median follow-up of 103 months, 79% of subjects were dead (bortezomib+PLD: 253 [78%]; bortezomib: 257 [80%]), 6% withdrew consent, 4% were lost to follow-up, and 11% were still alive. Median OS in bortezomib+PLD–treated subjects was 33.0 months (95% CI [28.9, 37.1]) versus 30.8 months (95% CI [25.2, 36.5]) in bortezomib-treated subjects (HR=1.05, 95% CI [0.88, 1.25]; p=0.6068). The types of salvage therapies utilized included dexamethasone (49.1%), thalidomide (31.0%), cyclophosphamide (28.5%), melphalan (22.9%), lenalidomide (21.8%), bortezomib (20.4%) and doxorubicin (8.0%), which were well-balanced between the two treatment groups.

Conclusion

Despite inducing a superior TTP, long-term follow-up revealed that PLD+bortezomib-treatment did not improve the OS compared with bortezomib alone in subjects with relapsed or refractory MM. The inability to confirm the early survival advantage may be due to the effects of subsequent lines of therapy, and underscores the need for long-term follow-up of phase III trials.