The comprehensive clinical management of multiple myeloma and related-plasma cell disorders

Whilst we think of multiple myeloma and related plasma cell disorders as incurable to date, never before has there been such hope and enthusiasm about advances in the research and treatment of these various diseases. Translational research is very much at the forefront of progress for further refining targeted therapies and continuing to improve clinical efficacy. Whilst some of these advances in the last decade have been truly dramatic in their scope and timing, it is also worth noting that relatively incremental changes have favorably impacted on patient outcome, and this comprehensive clinical management review captures these accordingly. We hope therefore that this concise overview will give readers, be they specialist hemato-oncologists, or other providers and researchers in the field, an enlightening insight into the exciting future of therapeutic opportunities, as well as a practical 'hands on' approach.

Response evaluation and monitoring of multiple myeloma

Monitoring multiple myeloma (MM) is essential during the evaluation of response to each therapy line, after transplantation and at the time of relapse or progression in all patients. An initial complete workup, including appropriate protein studies in serum and urine is mandatory. The use of uniform criteria is particularly important in the context of clinical trials. Complete remission (CR) definition, the goal for the majority of patients, is now in constant evolution, with immunophenotypic and molecular minimal residual disease measurement in bone marrow as well as imaging techniques. Identification of relapse/progression with traditional and novel techniques for eventual prompt intervention with rescue treatment is a current issue of debate.

European perspective on multiple myeloma treatment strategies in 2014

The treatment of multiple myeloma has undergone significant changes and has resulted in the achievement of molecular remissions, the prolongation of remission duration, and extended survival becoming realistic goals, with a cure being possible in a small but growing number of patients. In addition, nowadays it is possible to categorize patients more precisely into different risk groups, thus allowing the evaluation of therapies in different settings and enabling a better comparison of results across trials. Here, we review the evidence from clinical studies, which forms the basis for our recommendations for the management of patients with myeloma. Treatment approaches depend on "fitness," with chronological age still being an important discriminator for selecting therapy. In younger, fit patients, a short three drug-based induction treatment followed by autologous stem cell transplantation (ASCT) remains the preferred option. Consolidation and maintenance therapy are attractive strategies not yet approved by the European Medicines Agency, and a decision regarding post-ASCT therapy should only be made after detailed discussion of the pros and cons with the individual patient. Two- and three-drug combinations are recommended for patients not eligible for transplantation. Treatment should be administered for at least nine cycles, although different durations of initial therapy have only rarely been compared so far. Comorbidity and frailty should be thoroughly assessed in elderly patients, and treatment must be adapted to individual needs, carefully selecting appropriate drugs and doses. A substantial number of new drugs and novel drug classes in early clinical development have shown promising activity. Their introduction into clinical practice will most likely further improve treatment results.

Phase 2 randomized study of bortezomib-melphalan-prednisone with or without siltuximab (anti-IL-6) in multiple myeloma

Because interleukin-6 (IL-6) is considered important in the proliferation of early multiple myeloma (MM), we hypothesized that the addition of the anti-IL-6 monoclonal antibody siltuximab to the bortezomib-melphalan-prednisone (VMP) regimen would improve outcomes in transplant-ineligible patients with newly diagnosed MM. One hundred and six patients were randomized to receive 9 cycles of VMP or VMP plus siltuximab (11 mg/kg every 3 weeks) followed by siltuximab maintenance. Baseline characteristics were well balanced except for immunoglobulin A subtype and 17p deletions. With a complete response (CR) rate of 27% on siltuximab plus VMP (S+VMP) and 22% on VMP, the study did not confirm its hypothesis that the addition of siltuximab would increase the CR rate by at least 10%. Overall response rate was 88% on S+VMP and 80% on VMP, and at least very good partial response rates were 71% and 51% (P = .0382), respectively. Median progression-free survival (17 months) and 1-year overall survival (88%) were identical in the 2 arms. Grade ≥3 adverse-event incidence was 92% on S+VMP and 81% on VMP (P = .09), with trends toward more hematologic events and infections on S+VMP. Maintenance therapy with siltuximab was well tolerated. In conclusion, the addition of siltuximab to VMP did not improve the CR rate or long-term outcomes. This study was registered at http://clinicaltrials.gov as #NCT00911859.

Combination of international scoring system 3, high lactate dehydrogenase, and t(4;14) and/or del(17p) identifies patients with multiple myeloma (MM) treated with front-line autologous stem-cell transplantation at high risk of early MM progression-related death

PURPOSE

To construct and validate among patients with multiple myeloma (MM) who were treated with intensive therapy a prognostic index of early MM progression-related death.

PATIENTS AND METHODS

Patient-level data from the Intergroupe Francophone du Myélome (IFM) 2005-01 trial (N = 482) were used to construct the prognostic index. The event was MM progression-related death within 2 years from treatment initiation. The index was validated using data from three other trials: the Gruppo Italiano Malattie Ematologiche dell' Adulto (GIMEMA) 26866138-MMY-3006 trial (N = 480), the Programa para el Estudio de la Terapéutica en Hemopatía Maligna (PETHEMA)-GEMMENOS65 trial (N = 390), and the Hemato-Oncologie voor Volwassenen Nederland (HOVON) -65/German-Speaking Myeloma Multicenter Group (GMMG) -HD4 trial (N = 827).

RESULTS

The risk of early MM progression-related death was related to three independent prognostic variables: lactate dehydrogenase (LDH) higher than than normal, International Staging System 3 (ISS3), and adverse cytogenetics [t(4;14) and/or del(17p)]. These three variables enabled the definition of an ordinal prognostic classification composed of four scores (0 to 3). Patients with a score of 3, defined by the presence of t(4;14) and/or del(17p) in addition to ISS3 and/or high LDH, comprised 5% (20 of 387 patients) to 8% (94 of 1,139 patients) of the patients in the learning and validation samples, respectively, and they had a very poor prognosis. When applied to the population of 855 patients who had received bortezomib-based induction therapy in the four trials, the prognostic classification was also able to segregate patients into four categories, with a very poor prognosis attributed to patients with a score of 3.

CONCLUSION

Our model allows the simple definition of a subgroup of MM patients at high risk of early MM progression-related death despite the use of the most modern and effective strategies.

Transcriptome analysis reveals molecular profiles associated with evolving steps of monoclonal gammopathies

A multistep model has been proposed of disease progression starting in monoclonal gammopathy of undetermined significance continuing through multiple myeloma, sometimes with an intermediate entity called smoldering myeloma, and ending in extramedullary disease. To gain further insights into the role of the transcriptome deregulation in the transition from a normal plasma cell to a clonal plasma cell, and from an indolent clonal plasma cell to a malignant plasma cell, we performed gene expression profiling in 20 patients with monoclonal gammopathy of undetermined significance, 33 with high-risk smoldering myeloma and 41 with multiple myeloma. The analysis showed that 126 genes were differentially expressed in monoclonal gammopathy of undetermined significance, smoldering myeloma and multiple myeloma as compared to normal plasma cell. Interestingly, 17 and 9 out of the 126 significant differentially expressed genes were small nucleolar RNA molecules and zinc finger proteins. Several proapoptotic genes (AKT1 and AKT2) were down-regulated and antiapoptotic genes (APAF1 and BCL2L1) were up-regulated in multiple myeloma, both symptomatic and asymptomatic, compared to monoclonal gammopathy of undetermined significance. When we looked for those genes progressively modulated through the evolving stages of monoclonal gammopathies, eight snoRNA showed a progressive increase while APAF1, VCAN and MEGF9 exhibited a progressive downregulation. In conclusion, our data show that although monoclonal gammopathy of undetermined significance, smoldering myeloma and multiple myeloma are not clearly distinguishable groups according to their gene expression profiling, several signaling pathways and genes were significantly deregulated at different steps of the transformation process.

Differential humoral responses against heat-shock proteins after autologous stem cell transplantation in multiple myeloma

Heat-shock proteins (HSP) are important molecules in the pathogenesis of multiple myeloma (MM). Their blockages by drugs or cellular immune response have been investigated, and a possible association with the presence of oligoclonal bands (OB) has been postulated in patients with MM after allogenic stem cell transplantation. The aim of the present study was to ascertain the serum antibody levels against three HSP (60, 70 and 90) by ELISA in patients with MM in complete remission after autologous stem cell transplantation (ASCT), with or without OB, and compare them with those patients with stable gammopathy of undetermined significance (MGUS) and healthy controls. Our results in samples after ASCT showed no differential levels of anti-HSP according to the presence or absence of the oligoclonal response. However, higher levels of anti-HSP90 were found in patients with stable MGUS in comparison with MM patients (p = 0.004). In the same line, a longer progression-free survival was observed in those patients who presented higher anti-HSP90 levels after ASCT (p = 0.042). These results suggest, for first time, the potential of anti-HSP90 humoral immune response for long-term control of malignant plasma cell disorders.

Phase Ib Study of Panobinostat and Bortezomib in Relapsed or Relapsed and Refractory Multiple Myeloma

Purpose

Despite advancements, prognosis for patients with relapsed/refractory multiple myeloma (MM) is poor, and novel therapies are needed. Panobinostat is a potent deacetylase inhibitor that elicits synergistic effects on MM cells in combination with bortezomib. This phase Ib study sought to determine the maximum-tolerated dose (MTD) of panobinostat plus bortezomib in patients with relapsed or relapsed and refractory MM.

Patients and Methods

In the dose-escalation phase (n = 47), panobinostat was administered orally thrice weekly every week in combination with bortezomib (21-day cycles). After MTD determination, patients were evaluated in an expansion phase (n = 15) that incorporated a 1-week treatment holiday of panobinostat, with dexamethasone added in cycle 2. Additional assessments included safety, pharmacokinetics, and efficacy per International Myeloma Working Group criteria.

Results

The MTD was established at panobinostat 20 mg plus bortezomib 1.3 mg/m2. Grade 3 or 4 adverse events (AEs) included thrombocytopenia (85.1%), neutropenia (63.8%), and asthenia (29.8%) in the escalation phase, and thrombocytopenia (66.7%), neutropenia (46.7%), and fatigue (20.0%) in the expansion phase. At MTD in the escalation phase, eight patients (47.1%) discontinued therapy as a result of AEs, whereas five patients (33.3%) discontinued treatment in the expansion phase. Expansion phase patients demonstrated greater median treatment duration. Overall response rate (ORR) was 73.3% in the expansion phase and 52.9% at the escalation phase MTD. Among bortezomib-refractory patients, the ORR was 26.3%, and 42.1% of patients had ≥ minimal response.

Conclusion

The MTD of panobinostat plus bortezomib was determined and demonstrated activity in patients with relapsed or relapsed/refractory MM, including bortezomib-refractory patients. A phase II/III clinical trial program (Panobinostat or Placebo With Bortezomib and Dexamethasone in Patients With Relapsed Multiple Myeloma [PANORAMA]) has been initiated.

Pattern of relapse and progression after autologous SCT as upfront treatment for multiple myeloma

The achievement of CR is the crucial step for a prolonged PFS and OS after an autologous SCT in multiple myeloma (MM). Unfortunately, even with the use of new regimens and the current high CR rates, most, if not all, patients will ultimately relapse or progress. We analyzed the type of relapse or progression (asymptomatic vs symptomatic), clinical features including the presence of extramedullary involvement and time to next treatment in 211 patients who underwent melphalan-based autologous SCT over an 18-year period at our institution. After autologous SCT, serological or asymptomatic relapse/progression was observed in about one half of the patients. The treatment-free interval was significantly longer in patients relapsing from CR than in those progressing from PR (P=0.017). Patients with serological relapse/progression had a significantly longer OS than those relapsing from symptomatic disease (P=0.002). The relapse pattern was similar to the initial clinical presentation. Survival after relapse/progression was shorter in those patients with a 24-h urine M-protein excretion of at least 200 mg (P=0.048). Extramedullary involvement was frequent (24%), being the highest risk in patients with extramedullary involvement at diagnosis (P=0.001).

Evaluating gene expression profiling by quantitative polymerase chain reaction to develop a clinically feasible test for outcome prediction in multiple myeloma

The gene expression profiles (GEPs) of 96 selected genes were analysed by real-time quantitative polymerase chain reaction (qPCR) with a TaqMan low-density array card in isolated tumour plasma cells (PCs) from 157 newly diagnosed multiple myeloma (MM) patients. This qPCR-based GEP correctly classified cases following the Translocation-cyclin D classification. Classic prognostic parameters and qPCR-based GEP predicted MM patient outcome and, although multivariate analyses revealed that cytogenetic risk (standard vs. high risk) was the variable that most strongly predicted prognosis, GEP added significant information for risk stratification. Considering only the standard risk cytogenetic patients, multivariate analyses revealed that high β2-microglobulin, low CDKN1A and high SLC19A1 gene expression levels independently predicted a short time-to-progression (TTP), while high International Staging System stage, low CDKN2B and high TBRG4 gene expression predicted poor overall survival (OS). A gene expression risk score enabled the division of standard risk patients into two groups with different TTPs (83% vs. 38% at 3 years, P < 0·0001) and OS rates (88% vs. 61% at 5 years; P = 0·003). This study demonstrates that quantitative PCR is a robust, accurate and feasible technique for implementing in the daily routine as a surrogate for GEP-arrays.

Lenalidomide plus dexamethasone for high-risk smoldering multiple myeloma

BACKGROUND

For patients with smoldering multiple myeloma, the standard of care is observation until symptoms develop. However, this approach does not identify high-risk patients who may benefit from early intervention.

METHODS

In this randomized, open-label, phase 3 trial, we randomly assigned 119 patients with high-risk smoldering myeloma to treatment or observation. Patients in the treatment group received an induction regimen (lenalidomide at a dose of 25 mg per day on days 1 to 21, plus dexamethasone at a dose of 20 mg per day on days 1 to 4 and days 12 to 15, at 4-week intervals for nine cycles), followed by a maintenance regimen (lenalidomide at a dose of 10 mg per day on days 1 to 21 of each 28-day cycle for 2 years). The primary end point was time to progression to symptomatic disease. Secondary end points were response rate, overall survival, and safety.

RESULTS

After a median follow-up of 40 months, the median time to progression was significantly longer in the treatment group than in the observation group (median not reached vs. 21 months; hazard ratio for progression, 0.18; 95% confidence interval [CI], 0.09 to 0.32; P<0.001). The 3-year survival rate was also higher in the treatment group (94% vs. 80%; hazard ratio for death, 0.31; 95% CI, 0.10 to 0.91; P=0.03). A partial response or better was achieved in 79% of patients in the treatment group after the induction phase and in 90% during the maintenance phase. Toxic effects were mainly grade 2 or lower.

CONCLUSIONS

Early treatment for patients with high-risk smoldering myeloma delays progression to active disease and increases overall survival. (Funded by Celgene; ClinicalTrials.gov number, NCT00480363.).

Bortezomib-based versus nonbortezomib-based induction treatment before autologous stem-cell transplantation in patients with previously untreated multiple myeloma: a meta-analysis of phase III randomized, controlled trials

PURPOSE

To characterize efficacy and safety of bortezomib-based versus nonbortezomib-based induction regimens through an integrated analysis of data from phase III studies in transplantation-eligible patients with previously untreated myeloma.

PATIENTS AND METHODS

Patient-level data from the IFM 2005-01 (bortezomib-dexamethasone v vincristine-doxorubicin-dexamethasone [VAD] induction), HOVON-65/GMMG-HD4 (bortezomib-doxorubicin-dexamethasone v VAD), and PETHEMA GEM05MENOS65 (bortezomib-thalidomide-dexamethasone v thalidomide-dexamethasone) studies were pooled in an integrated analysis of efficacy and safety. Study-level data from the GIMEMA MM-BO2005 study (bortezomib-thalidomide-dexamethasone v thalidomide-dexamethasone) supplemented the integrated patient-level analysis. Key efficacy end points were post-transplantation complete plus near-complete response (CR+nCR) rate and progression-free survival (PFS).

RESULTS

Patient-level data for 1,572 patients (bortezomib-based induction, n = 787; nonbortezomib-based induction, n = 785) were included. Post-transplantation CR+nCR rate was significantly higher following bortezomib-based versus nonbortezomib-based induction (38% v 24%; odds ratio, 2.05; P < .001); the benefit remained similar (pooled odds ratio, 1.96) when GIMEMA MM-BO2005 data were included. Median PFS was 35.9 months versus 28.6 months with bortezomib-based versus nonbortezomib-based induction, respectively (hazard ratio, 0.75; P < .001); 3-year overall survival (OS) rates were 79.7% and 74.7%, respectively (hazard ratio for OS, 0.81; P = .0402). Median duration of induction treatment was 11 weeks in both treatment groups. Rates of peripheral neuropathy during induction were 34% versus 17% (grade ≥ 3, 6% v 1%). Overall, 3% and 4% of patients died during bortezomib-based and nonbortezomib-based induction, respectively.

CONCLUSION

Bortezomib-based induction results in significant improvements in response and PFS/OS compared with nonbortezomib-based induction and is generally well tolerated, with a higher rate of peripheral neuropathy but no apparent increase in risk of death during induction.

Natural history and prognostic impact of oligoclonal humoral response in patients with multiple myeloma after autologous stem cell transplantation: long-term results from a single institution

The emergence of an oligoclonal humoral response, resulting in the appearance of a different serum M-protein to that observed at diagnosis is a well-recognized event after autologous stem cell transplantation in multiple myeloma in complete response, and it has been considered to be a benign phenomenon. The aim of the present study was to investigate the incidence, biological characteristics and prognostic value of the oligoclonal bands in patients with myeloma who underwent autologous transplantation at our institution in the last 18 years. We proceed with a retrospective systematic review of all serum and urine immunofixation studies performed in the 211 patients with multiple myeloma who underwent melphalan-based autologous transplantation. Oligoclonal bands were observed in 34% of the patients, with a significantly higher prevalence with the use of novel agents versus conventional chemotherapy in induction (63% vs. 22%; P=0.0001). The incidence of oligoclonal bands was most frequent in non-IgG isotype, particularly in light chain only myeloma. The oligoclonal phenomenon was almost exclusive to patients in complete remission compared to other degrees of response (87% vs. 13%; P=0.0001), and lasted for a median of 1.35 years, persisting during follow up in all patients except in those who relapsed. In prognostic terms, the presence of oligoclonality resulted in a significantly longer progression-free and overall survival. Patients with oligoclonal humoral response lasting for more than one year after transplantation had a significantly longer clinical progression-free and overall survival than those with shorter duration (P=0.008 and P=0.0001, respectively), likely reflecting the importance of a robust humoral immune response.

Impact of global and gene-specific DNA methylation pattern in relapsed multiple myeloma patients treated with bortezomib

We studied seventy-five patients with relapsed MM treated with bortezomib-based regimens. DNA was isolated from bone marrow samples at the time of relapse. Global methylation was determined by ELISA, and CpG island DNA methylation profile of 30 genes by a DNA methylation PCR system. Patients with more than 3.95% of total DNA methylated achieved better overall survival (OS) (p=0.004). A relatively low methylation percentage (<1.07%) of NFKB1 was also associated with longer OS after bortezomib treatment (p=0.015). The combination of highly methylated global genome with low NFKB1 methylation status defined a specific subset of patients with better prognosis.

A prospective, international phase 2 study of bortezomib retreatment in patients with relapsed multiple myeloma

Multiple myeloma (MM) typically follows a relapsing course with many patients requiring multiple therapies. This single-arm phase 2 study prospectively evaluated the efficacy and safety of bortezomib retreatment in MM patients who had relapsed after achieving at least a partial response (≥ PR) to prior bortezomib-based therapy. Patients aged ≥ 18 years, with measurable, secretory MM, who relapsed ≥ 6 months after prior bortezomib treatment were eligible. Patients received up to eight cycles of bortezomib (± dexamethasone). The primary endpoint was best confirmed response at retreatment; secondary endpoints included duration of response (DOR), time to progression (TTP), and safety. Adverse events (AEs) were graded by National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. A total of 130 patients (median of two prior lines of therapy) were enrolled and received retreatment. At retreatment, 28% and 72% of patients received bortezomib and bortezomib-dexamethasone, respectively. Overall response rate was 40%. In patients who achieved ≥ PR, median DOR and TTP were 6.5 and 8.4 months, respectively. Thrombocytopenia was the most common grade ≥ 3 AE (35%). Forty percent of patients experienced neuropathy events, which improved and resolved in a median of 1.5 and 8.9 months, respectively. In conclusion, bortezomib retreatment was effective and tolerable in relapsed MM patients, with no evidence of cumulative toxicities.

Plasma cell leukemia: consensus statement on diagnostic requirements, response criteria and treatment recommendations by the International Myeloma Working Group

Plasma cell leukemia (PCL) is a rare and aggressive variant of myeloma characterized by the presence of circulating plasma cells. It is classified as either primary PCL occurring at diagnosis or as secondary PCL in patients with relapsed/refractory myeloma. Primary PCL is a distinct clinic-pathological entity with different cytogenetic and molecular findings. The clinical course is aggressive with short remissions and survival duration. The diagnosis is based upon the percentage (≥ 20%) and absolute number (≥ 2 × 10(9)/l) of plasma cells in the peripheral blood. It is proposed that the thresholds for diagnosis be re-examined and consensus recommendations are made for diagnosis, as well as, response and progression criteria. Induction therapy needs to begin promptly and have high clinical activity leading to rapid disease control in an effort to minimize the risk of early death. Intensive chemotherapy regimens and bortezomib-based regimens are recommended followed by high-dose therapy with autologous stem cell transplantation if feasible. Allogeneic transplantation can be considered in younger patients. Prospective multicenter studies are required to provide revised definitions and better understanding of the pathogenesis of PCL.

Multiparameter flow cytometry evaluation of plasma cell DNA content and proliferation in 595 transplant-eligible patients with myeloma included in the Spanish GEM2000 and GEM2005<65y trials

The incorporation of high-dose therapy/autologous stem cell transplantation (HDT/ASCT) and novel agents has significantly improved survival in patients with multiple myeloma (MM), but whether this improvement also benefits patients harboring poor prognostic features, such as nonhyperdiploid MM (NH-MM) and a high proliferation index, remains largely unknown. We analyzed the DNA content and proliferation index of bone marrow plasma cells (PCs) by multiparameter flow cytometry in 595 newly diagnosed transplant-eligible patients with MM included in two consecutive PETHEMA/GEM trials: GEM2000 [VBMCP/VBAD (vincristine, carmustine, melphalan, cyclophosphamide, prednisone/vincristine, bischloroethylnitrosourea, adriamycin, and dexamethasone) followed by HDT/ASCT; n = 319] and GEM2005<65y (randomized induction with VBMCP/VBAD/bortezomib or thalidomide/dexamethasone or bortezomib/thalidomide/dexamethasone followed by HDT/ASCT; n = 276). Of the 595 patients, 295 were classified as NH-MM (49.6%) and 336 (56.5%) as high-proliferative MM (≥1% PCs in S-phase). Detection of NH-MM DNA content and ≥1% PCs in S-phase were of independent prognostic value for overall survival. Treatment with bortezomib-based regimens abrogated the inferior overall survival of patients with ≥1% PCs in S-phase but not of patients with NH-MM. Finally, a comparative analysis of PC proliferation index at diagnosis versus disease progression showed a twofold increase at relapse in 44 of 52 patients (85%) analyzed at both time points. NH-MM and a high proliferation index assessed by multiparameter flow cytometry remain as independent prognostic factors in MM, but the latter may be overcome by incorporating novel agents in the HDT/ASCT setting.

Evolving chemotherapy options for the treatment of myeloma kidney: a 40-year perspective

Kidney impairment (KI) at the time of initial diagnosis is common in myeloma. The improvement of kidney function and the reversal of KI are of utmost importance. Recent advances have made it possible to reverse acute kidney damage due to myeloma in most patients, at least if treatment is immediately implemented. Immediate antimyeloma therapy and appropriate hydration are the most commonly used treatment modalities for the management of acute KI related to myeloma. Mechanical approaches can only temporarily reduce the free light-chain load, and without effective chemotherapy they are probably not able to significantly improve kidney function. However, the role of mechanical approaches together with effective chemotherapy is still being explored. Thalidomide, lenalidomide, and bortezomib have improved the survival of myeloma patients, but they have also improved the outcome of patients presenting with KI. Thalidomide is safe to use on patients with KI without dose adjustments. Lenalidomide needs dose modification, but it can improve kidney function in many patients. Bortezomib seems to be the agent of choice for most patients presenting with KI without dose modifications. This review focuses on the management of patients presenting with "myeloma kidney" using modern chemotherapy approaches, especially novel agents.

Intravenous busulfan and melphalan as a conditioning regimen for autologous stem cell transplantation in patients with newly diagnosed multiple myeloma: a matched comparison to a melphalan-only approach

Melphalan 200 mg/m(2) (MEL200) is the standard conditioning regimen administered to newly diagnosed patients with multiple myeloma (MM) undergoing autologous stem cell transplantation (ASCT). Few alternatives have been explored in order to improve the antimyeloma activity of this conditioning. We compare i.v. busulfan (BU) 9.6 mg/kg and MEL 140 mg/m(2) (MEL140) versus MEL200 mg/m(2) as a conditioning regimen before ASCT for newly diagnosed patients with MM. For this purpose, 51 patients receiving i.v. BU plus MEL were compared to 102 patients receiving MEL200 mg/m(2) in a 1:2 matched control analysis. Matching criteria included age, clinical stage at diagnosis, and response to induction therapy. No differences in the overall and complete response (CR) rates were observed after ASCT between both groups. After a median follow-up of 63 and 50 months in control and BU plus MEL groups, progression-free survival (PFS) was 24 and 33 months, respectively (P = .10). Most frequent toxicities included mucositis and febrile neutropenia in both groups. No case of sinusoidal obstruction syndrome was observed. Transplant-related mortality was 4% and 2% in BU plus MEL and control groups, respectively. ASCT conditioned with i.v. BU plus MEL may be considered an effective and well-tolerated alternative to a MEL-only approach as a conditioning regimen for patients with MM who are candidates for ASCT.