Molecular Remission After Bortezomib-Thalidomide-Dexamethasone Compared with Thalidomide-Dexamethasone as Consolidation Therapy Following Double Autologous Transplantation for Multiple Myeloma: Results of a Qualitative and Quantitative Analysis

Abstract 861

The high rate of complete response (CR) effected by novel agents as induction and consolidation/maintenance therapy in multiple myeloma (MM) has renewed interest in the evaluation of minimal residual disease (MRD) after these combined treatment strategies. For this purpose, a useful molecular marker is represented by the immunoglobulin heavy-chain (IgH) rearrangement which can be carefully detected by means of polymerase chain reaction (PCR). We designed a molecular sub-study to the phase 3 GIMEMA trial of bortezomib-thalidomide-dexamethasone (VTD) vs. thalidomide-dexamethasone (TD) incorporated into double autologous stem cell transplantation (ASCT) for newly diagnosed MM. By study design, patients randomized at diagnosis to VTD or TD as induction therapy before ASCT received two 35-day cycles of consolidation therapy with VTD or TD starting 3 months after ASCT(s), independently from prior response. Doses of study drugs were the following: V, 1.3 mg/m² once weekly; T, 100 mg/d through d 1 to 70; D, 320 mg/cycle. Aim of the molecular study was to compare the activity of VTD consolidation with that of TD by qualitative and quantitative PCR analysis. Patients who were planned to receive consolidation with either VTD or TD and who were in confirmed CR or near CR before the start of consolidation therapy were eligible for entry into the molecular study. A qualitative and quantitative PCR analysis with patient-specific primers was performed on bone marrow samples collected at day 0 and at day +70 after the two preplanned cycles of either VTD or TD. At this time, 84 patients were included in the study; of these, 67 patients were analyzed for MRD detection based on the availability of: 1) a molecular marker (e.g. IgH rearrangement) assessed at diagnosis; 2) both pre- and post-consolidation bone marrow samples. According to randomization at diagnosis, 35 out of 67 patients received VTD consolidation, while TD consolidation was given to 32 patients. Qualitative PCR analysis performed on bone marrow samples collected at day 0 showed that MRD before the start of VTD consolidation therapy was undetectable in 15 out of 35 patients, or 43%; the corresponding value before the start of TD consolidation was 37.5% (or 12 out of 32 patients). In comparison with the pre-consolidation status, analysis of bone marrow samples collected at day +70 revealed an upgrade in PCR-negativity from 37.5% to 52% with TD consolidation and from 43% to 67% with VTD consolidation (p=0.05, according to McNemar's test). By using the Fisher's exact test, the proportion of patients with post-consolidation PCR-negativity was significantly higher with VTD vs. TD consolidation (p=0.05). These data were furtherly extended by a Real-time quantitative PCR analysis, which could be performed in 45 out of the 67 patients initially included in the study (22 in the TD arm and 23 in VTD). In comparison with residual tumor mass at day 0, quantitative PCR analysis of bone marrow samples collected at day +70 revealed a median 1 log reduction in tumor burden with TD consolidation vs. a median 5 log reduction with VTD consolidation. By using the Wilcoxon test, the overall reduction in residual tumor burden effected by VTD consolidation therapy was statistically significant (p=0.05). In conclusion, in comparison with TD consolidation, two 35-day cycles of consolidation therapy with VTD following double ASCT significantly increased the rate of molecular remissions and significantly reduced the burden of residual myeloma cells persisting after ASCT. Superior activity of VTD over TD consolidation was retained although prior exposure to the same regimen given as induction therapy in preparation for ASCT. Additional data on molecular follow-up analyses of bone marrow samples collected after day +70 and comparisons of the prognostic relevance of PCR-negativity with PCR-positivity, as well as of PCR-negativity induced by VTD with that induced by TD will be presented during the meeting.

Supported by: Progetto di Ricerca Finalizzata Orientata (to M.C), BolognAIL, Fondazione del Monte di Bologna e Ravenna.