The Effect of Paraprotein Heavy Chain and Free Light Chain Types on the Efficacy of Pegylated Liposomal Doxorubicin + Bortezomib Versus Bortezomib Alone in Patients with Relapsed/Refractory Multiple Myeloma

Background: Many factors influence the choice of salvage therapy in relapsed/refractory multiple myeloma (RRMM), including various disease characteristics such as light chain and heavy chain subtypes. Patients with light chain only myeloma are a biologically and phenotypically distinct subset of patients from those with IgG, IgA, IgM, or IgD disease. Evidence exists that the presence of different paraprotein heavy and light chain subtypes may affect treatment outcomes. We investigated the effect of the presence of paraprotein heavy and light chain types on the efficacy and safety of pegylated liposomal doxorubicin (PLD) + bortezomib (B) versus B alone based on the phase III randomized trial of PLD+B vs. B alone in RRMM, which demonstrated improved time to progression (TTP) with PLD+B (Orlowski, JCO 2007).

Methods: Eligible patients were randomized to bolus IV B 1.3 mg/m2 on days 1, 4, 8, and 11 of each 3-week cycle (n=322) or to the same B regimen plus IV PLD 30 mg/m2 on day 4 (n=324) of each cycle. The subsets of patients with light chain and heavy chain multiple myeloma subtypes were analyzed retrospectively.

Results: The presence of light chain myeloma was observed in 77 patients. Few patients had IgM/IgD subtype myeloma (4 and 6 patients, respectively), while the majority of patients had IgG (n=379) or IgA (n=265) subtypes. Time to disease progression (TTP) and complete response (CR) + partial response (PR) rates for PLD+B vs B alone in patients with light chain, IgG, and IgA myeloma subtypes are listed in the table.

Results showed that the combination of PLD+B had significant benefit over B alone in TTP (PLD+B led to longer TTP than B alone) for IgG paraprotein and light chain subtypes. Safety profiles for the 2 regimens in these subsets of patients with heavy or light chain myeloma were consistent with the known toxicities of the 2 agents used.

Conclusions: These data demonstrate that the combination of PLD+B is an important treatment option in patients with RRMM. Patients with light chain only disease had the largest incremental benefit from the addition of PLD with an absolute increase in TTP of 159 days as well as an increase in the overall response rate from 30% to 56%.