Long-Term Follow-Up of Patients Treated with Bortezomib Alone and in Combination with Dexamethasone as Frontline Therapy for Multiple Myeloma.

Introduction: Novel therapeutic agents, such as bortezomib (VELCADE^®; btz), thalidomide, and lenalidomide, are being used in combination with dexamethasone (dex) as frontline therapies in MM. Phase 2 and 3 trials with limited follow-up have reported a high response rate and feasibility of high-dose therapy and stem cell transplantation (HDT-SCT). Here we present longer follow-up on our phase 2 trial of btz±dex as frontline therapy.

Methods: Patients (pts) with measurable disease and KPS ≥50% received btz 1.3mg/m² on days 1, 4, 8 and 11 of a 3-week cycle for up to 6 cycles. Oral dex 40mg was added on the day of and day after btz for pts achieving < partial response (PR) after 2 cycles or < complete response (CR) after 4 cycles. Responses were assessed using European Group for Blood and Marrow Transplantation criteria, with the addition of near CR (nCR; CR but positive immunofixation).

Results: 48 pts were accrued and were evaluable for response; a further 2 registered on the trial declined to proceed. Median age was 60 years, 46% were male, 64% had IgG and 21% IgA, and 50% were Durie-Salmon stage III. At the end of btz±dex treatment, overall response rate (ORR; CR+nCR+PR) was 90% with 19% CR/nCR; an additional 8% achieved a minimal response (MR). Response to btz alone was rapid; response rate by end of cycle 2 was 50%, including 10% CR/nCR. Dex was added for 36 (75%) pts: 17 at cycle 3, 18 at cycle 5, and 1 at cycle 6. Addition of dex improved best responses to btz in 23 (64%) pts, with 12 improving from stable disease to MR or PR, 9 from MR to PR, 1 from PR to nCR, and 1 from nCR to CR. Median time to best response was 1.9 months. For all 48 pts, with a median follow-up of 24 months, median time to alternative therapy (TTAT) was 7 months (range: 2–25; this includes pts who went on to HDT-SCT), and median overall survival (OS) has not been reached; 1-year survival rate was 90%. For pts not proceeding to HDT-SCT, median TTAT was 22 months, median OS has not been reached; 1-year survival rate was 80%. 23/48 pts proceeded to HDT-SCT. Median CD34+ harvest was 12.6 x 10⁶ cells/kg (range: 5.1–40.4 x 10⁶) from a median of 2 collection days (range: 1–8). All pts had complete hematologic recovery; median time to neutrophil (ANC >1000/mm³) and platelet (>100,000/mm³) engraftment was 11 days (range: 8–13) and 17 days (range: 10–98), respectively. In the 23 HDT-SCT pts, median TTAT and OS have not been reached; post-transplant 1-year survival rate was 90%. The most common grade ≥2 adverse events for btz±dex were sensory neuropathy/neuropathic pain (37%), fatigue (20%), constipation (16%), nausea (12%), and neutropenia (12%). Two pts developed grade 4 events (1 neutropenia, 1 thrombocytopenia).

Conclusion: Btz±dex is an effective frontline therapy for MM, with an ORR of 90%, including 19% CR/nCR, and OS rate of 80% at 1 year. The treatment is well tolerated and toxicities were manageable and reversible. Addition of dex to btz provides improved responses. TTAT for patients not undergoing HDT-SCT was 22 months. The regimen does not prejudice subsequent HDT-SCT; stem cell harvest and engraftment were successful in all pts proceeding to transplant. Consolidation with HDT-SCT further increases the response rate and durability of response. Btz+dex is being compared to VAD as induction therapy prior to HDT-SCT in a phase 3 study.