Major tumor shrinking and persistent molecular remissions after consolidation with bortezomib, thalidomide, and dexamethasone in patients with autografted myeloma

PURPOSE We investigated the effect on minimal residual disease, by qualitative and real-time quantitative polymerase chain reaction (RQ-PCR), of a consolidation regimen that included bortezomib, thalidomide, and dexamethasone (VTD) in patients with multiple myeloma (MM) responding to autologous stem-cell transplantation (auto-SCT). PATIENTS AND METHODS Patients achieving at least very good partial response who had an available molecular marker based on the immunoglobulin heavy-chain rearrangement received four courses of treatment every month: four infusions per month of bortezomib at 1.6 mg/m(2), thalidomide at 200 mg/d, and dexamethasone at 20 mg/d on days 1 to 4, 8 to 11, and 15 to 18. Patients were studied with tumor-clone-specific primers by qualitative nested PCR and RQ-PCR. Results Of 39 patients enrolled, 31 received the four VTD courses. Immunofixation complete responses increased from 15% after auto-SCT to 49% after VTD. Molecular remissions (MRs) were 3% after auto-SCT and 18% after VTD. Median time to maximum response was 3.5 months. So far, no patient in MR has relapsed (median follow-up, 42 months). VTD consolidation induced an additional depletion of 4.14 natural logarithms of tumor burden by RQ-PCR. Patients with a tumor load less than the median value after VTD had outcomes better than those who had tumor loads above the median value after VTD (at median follow-up: progression-free survival, 100% v 57%; P < .001). CONCLUSION To the best of our knowledge, this study is the first to document the occurrence of persistent MRs in a proportion of MM patients treated without allogeneic transplantation. Moreover, the major reduction in tumor load recorded by RQ-PCR after VTD suggests that unprecedented levels of tumor cell reduction can be achieved in MM thanks to the new nonchemotherapeutic drugs.