Advances in the Treatment of Multiple Myeloma
Focus on Bortezomib and LenalidomideA Growing Body of Evidence Suggests Efficacy in the Front-Line Setting
Both bortezomib (Velcade) and lenalidomide (Revlimid) are FDA-approved treatments for use in patients with multiple myeloma (MM) who have received at least one year of prior therapy. Lenalidomide is approved for use in combination with dexamethasone. Both agents—bortezomib with or without dexamethasone and lenalidomide with dexamethasone— are currently being investigated for use in the front-line setting, and a growing body of evidence suggests these agents can provide high response rates and consistently high rates of complete response (CR) in high-risk patients with no prior therapy.
Bortezomib is a 26S proteasome inhibitor. The 26S proteasome is a large protein complex that degrades ubiquinated proteins. The ubiquitin-proteasome pathway plays an essential role in regulating the intracellular concentration of specific proteins, thereby maintaining homeostasis within cells. Inhibition of the 26S proteasome prevents this targeted proteolysis, which can affect multiple signaling cascades within the cell. This disruption of normal homeostatic mechanisms can lead to cell death. The mechanism of action of lenalidomide—a thalidomide analogue with antiangiogenic, immunomodulatory, and antineoplastic properties—is less well characterized.Single-Agent Therapy With Bortezomib
In a Phase II study of bortezomib as a single agent in the front-line setting in patients eligible for stem-cell transplantation (SCT),1
the response rate was 40%, with a 10% complete and near-complete response (CR/nCR) rate. This is a considerable CR/nCR rate for a single-agent therapy in the front-line MM setting. Substantial single-agent activity was also demonstrated in patients with high-risk multiple myeloma (elevated b2-microglobulin, high plasma cell labeling index, or chromosome 13 deletion).2Combination Therapy With Bortezomib Plus Dexamethasone
Combination therapy with bortezomib plus dexamethasone has been investigated as induction therapy in three studies.3–5
In a Phase II study conducted by the Intergroupe Francophone du Mye’lome (IFM), the combination of bortezomib plus dexamethasone in patients with newly diagnosed MM resulted in a response rate of 67%, including a 21% CR/ nCR rate, prior to SCT.3 Among patients who proceeded to SCT, the post-SCT response rate was 90%, with a 33% CR/nCR rate.
Substantial activity was also reported in another study—one in which patients with newly diagnosed MM and were deemed eligible for SCT received bortezomib alone initially, with dexamethasone added later if response was suboptimal.4
In this study, the response rate was 90%, with a 19% CR/nCR rate. Among patients who proceeded to SCT, the one-year overall survival (OS) rate was 100%.
Preliminary results from an IFM Phase III study5
of bortezomib plus dexamethasone versus vincristine, doxorubicin, and dexamethasone (VAD) as induction therapy prior to SCT showed a greater postinduction response rate (82% vs. 67%) and CR/nCR rate (20% vs. 9%) with bortezomib plus dexamethasone. In addition, among patients who underwent a single SCT, a greater proportion of those who had received induction with bortezomib plus dexamethasone achieved a very good partial response (VGPR) or better (78% vs. 55%), eliminating the need for a second SCT.An Alternating Regimen of Bortezomib and Dexamethasone
Results of the first study in which bortezomib and dexamethasone were administered on an alternating basis were reported recently.6
Study enrollees were younger patients (<66 years of age) with newly diagnosed MM who were deemed eligible for SCT. The response rate was 82%, with 12% of patients achieving a CR and 10% achieving a VGPR. In general, response was rapid, with an 82% M-protein reduction achieved with the first 2 cycles.Bortezomib in Combination with Other Antineoplastic Agents
A Phase I/II study of bortezomib in combination with melphalan and prednisone (MP) was conducted in patients >65 years of age who were eligible for SCT.7
Approximately 50% of the study enrollees were >75 years of age. The response rate was 89%, with a CR/nCR rate of 43%. At 16 months, the rates of progression-free survival (PFS), event-free survival (EFS), and OS were 91%, 83%, and 90%, respectively. Approximately one-half of the patients who achieved a CR were determined to have achieved immunophenotypic remission (i.e., here were no detectable myeloma cells by multiparametric flow assay). Based on these excellent results, the triple regimen is now being compared with MP in an international Phase III trial.