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

Biological relapse in multiple myeloma: Outcome and treatment strategies in a Spanish real-world setting

Recommendations regarding the best time to start treatment in patients with relapsed/refractory multiple myeloma (RRMM) after biological relapse/progression (BR) are unclear. This observational, prospective, multicenter registry aimed to evaluate the impact on time to progression (TTP) of treatment initiation at BR versus at symptomatic clinical relapse (ClinR) based on the Spanish routine practice in adult patients with RRMM. Patients had two or less previous treatment lines and at least one previous partial response. Baseline characteristics and treatment outcomes were recorded, and survival was analyzed. Of 225 patients, 110 were treated at BR (TxBR group) and 115 at ClinR (TxClinR group) according to the investigators' criteria. The proportion of patients with higher ECOG, previous noncomplete remission (CR), and second relapse were significantly higher in the TxBR group compared to the TxClinR group. TheTxClinR group showed improved outcomes, including TTP, compared to the TxBR group. Progression-free survival increased in the TxClinR group (56.2 months) compared to the TxBR group (32.5 months) (p = 0.0137), and median overall survival also increased (p = 0.0897). Median TTP was significantly longer in patients relapsing from a CR (50.4 months) and in their first relapse (38.7 months) compared to those relapsing from a non-CR response (32.9 months) and in their second relapse (25.2 months). Physicians seemed to start treatment earlier in RRMM patients with poor prognosis features. Previous responses to anti-MM treatment and the number of prior treatment lines were identified as prognosis factors, whereby relapse from CR and first relapse were associated with a longer time to progression.

Machine Learning Approach for Rapid, Accurate Point-of-Care Prediction of M-Spike Values in Multiple Myeloma

PURPOSE

The gold standard for monitoring response status in patients with multiple myeloma (MM) is serum and urine protein electrophoresis which quantify M-spike proteins; however, the turnaround time for results is 3-7 days which delays treatment decisions. We hypothesized that machine learning (ML) could integrate readily available clinical and laboratory data to rapidly and accurately predict patient M-spike values.

METHODS

A retrospective chart review was performed using the deidentified, electronic medical records of 171 patients with MM.

RESULTS

Random forest (RF) analysis identified the weighted value of each independent variable (N = 43) integrated into the ML algorithm. Pearson and Spearman coefficients indicated that the ML-predicted M-spike values correlated highly with laboratory-measured serum protein electrophoresis values. Feature selected RF modeling revealed that only two variables-the first lagged M-spike and serum total protein-accurately predicted the M-spike.

CONCLUSION

Taken together, our results demonstrate the feasibility and prognostic potential of ML tools that integrate electronic data to longitudinally monitor disease burden. ML tools support the seamless, secure exchange of patient information to expedite and personalize clinical decision making and overcome geographic, financial, and social barriers that currently limit the access of underserved populations to cancer care specialists so that the benefits of medical progress are not limited to selected groups.

Optimal timing of treatment at relapse after autologous stem cell transplantation in patients with multiple myeloma: a study of the Korean Multiple Myeloma Working Party (KMM-1909)

The effectiveness of early treatment for biochemical relapse of multiple myeloma (MM) is unclear. To clarify this issue, this retrospective study was performed to evaluate the survival outcomes of 315 patients with relapsed MM after upfront autologous stem cell transplantation (ASCT). Over a median follow-up of 66.6 months (range, 15.1-195.5 months), 48.2% of patients showed biochemical relapse, 41.3% showed clinical relapse, and 10.5% showed significant biochemical relapse. Progression-free survival (PFS) and overall survival (OS) were inferior for patients with clinical relapse compared to the other patients. Multivariate analysis showed that clinical relapse was an independent prognostic factor for OS. In patients with biochemical relapse, there was no significant difference in survival between patients treated while asymptomatic and those treated once clinical symptoms had appeared. Relapse type after upfront ASCT was a significant prognostic factor in patients with MM. In addition, no survival benefit of early treatment at biochemical relapse was observed, but a triplet regimen may be beneficial for MM patients with biochemical relapse.

Relapse with plasmacytoma after upfront autologous stem cell transplantation in multiple myeloma

Please present P values consistently.Plasmacytoma has been reported to be associated with a poor prognosis in patients with multiple myeloma (MM). In this study, we evaluated the incidence of relapse with plasmacytoma and survival outcomes after upfront autologous stem cell transplantation (ASCT). This study retrospectively analyzed the data of 303 patients with MM who underwent upfront ASCT between April 2000 and April 2018 at eight institutes in the Republic of Korea. In total, 52 patients (17.1%) had plasmacytoma at MM relapse after upfront ASCT, of whom, 27 had paramedullary plasmacytoma (PMD) and 25 had extramedullary plasmacytoma (EMD). Patients with initial plasmacytoma were more likely to have plasmacytoma at MM relapse than those without initial plasmacytoma (37.1% vs. 11.2%). Over a median follow-up of 66.0 months, patients with plasmacytoma at relapse had significantly inferior overall survival (OS) than those without plasmacytoma (43.9 vs. 100.7 months, P < 0.001), but the OS did not significantly differ between patients with EMD and those with PMD (42.2 vs. 56.6 months, P=0.464). After MM relapse, all patients received salvage therapy, and progression-free survival after relapse was significantly shorter in patients with plasmacytoma than in those without (6.4 vs. 12.4 months, P = 0.007). This study showed that plasmacytoma frequently developed at MM relapse after upfront ASCT in patients with plasmacytoma at the time of diagnosis. Plasmacytoma at relapse was significantly associated with a poor prognosis.

Expert review on soft-tissue plasmacytomas in multiple myeloma: definition, disease assessment and treatment considerations

In this review, two types of soft-tissue involvement in multiple myeloma are defined: (i) extramedullary (EMD) with haematogenous spread involving only soft tissues and (ii) paraskeletal (PS) with tumour masses arising from skeletal lesions. The incidence of EMD and PS plasmacytomas at diagnosis ranges from 1·7% to 4·5% and 7% to 34·4% respectively. EMD disease is often associated with high-risk cytogenetics, resistance to therapy and worse prognosis than in PS involvement. In patients with PS involvement a proteasome inhibitor-based regimen may be the best option followed by autologous stem cell transplantation (ASCT) in transplant eligible patients. In patients with EMD disease who are not eligible for ASCT, a proteasome inhibitor-based regimen such as lenalidomide-bortezomib-dexamethasone (RVD) may be the best option, while for those eligible for high-dose therapy a myeloma/lymphoma-like regimen such as bortezomib, thalidomide and dexamethasone (VTD)-RVD/cisplatin, doxorubicin, cyclophosphamide and etoposide (PACE) followed by SCT should be considered. In both EMD and PS disease at relapse many strategies have been tried, but this remains a high-unmet need population.

Expert Panel Consensus Statement for Proper Evaluation of First Relapse in Multiple Myeloma

PURPOSE OF REVIEW

A working group of six expert physicians convened to assess the spectrum of multiple myeloma relapse presentations, discussed the features that can define the disease as aggressive and not aggressive, and established whether this information could help in selecting treatment together with the characteristics of disease and of patients and type of prior therapy.

RECENT FINDINGS

The working group agreed that relapse should be distinguished between biochemical and clinical according to IMWG. Moreover, the expert panel defined "aggressive disease" as a clinical condition that requires therapy able to induce a rapid and as deep as possible response to release symptoms and to avoid impending danger of new events. According to this definition, relapse was considered aggressive if it presents with at least one of the following features: doubling of M protein rate over 2 months, renal insufficiency, hypercalcemia, extramedullary disease, elevated LDH, high plasma cell proliferative index, presence of plasma cells in peripheral blood, or skeletal-related complications. Moreover, the panel agreed that this classification can be useful to choose therapy in first relapse together with other patient, disease, and prior therapy characteristics. So, this item was included in a new therapeutic algorithm. The treatment choice in MM at relapse is wider than in the past with the availability of many new therapeutic regimens leading to increased diversity of approaches and relevant risk of inappropriate treatment decisions. A practical classification of relapses into aggressive or non-aggressive, included in a decisional algorithm on MM management at first relapse, could help to make the appropriate treatment decisions.

c-MYC expression and maturity phenotypes are associated with outcome benefit from addition of ixazomib to lenalidomide-dexamethasone in myeloma

OBJECTIVES

In the TOURMALINE-MM1 phase 3 trial in relapsed/refractory multiple myeloma, ixazomib-lenalidomide-dexamethasone (IRd) showed different magnitudes of progression-free survival (PFS) benefit vs placebo-Rd according to number and type of prior therapies, with greater benefit seen in patients with >1 prior line of therapy or 1 prior line of therapy without stem cell transplantation (SCT).

METHODS

RNA sequencing data were used to investigate the basis of these differences.

RESULTS

The PFS benefit of IRd vs placebo-Rd was greater in patients with tumors expressing high c-MYC levels (median not reached vs 11.3 months; hazard ratio [HR] 0.42; 95% CI, 0.26, 0.66; P < .001) compared with in those expressing low c-MYC levels (median 20.6 vs 16.6 months; HR 0.75; 95% CI, 0.42, 1.2). Expression of c-MYC in tumors varied based on the number and type of prior therapy received, with the lowest levels observed in tumors of patients who had received 1 prior line of therapy including SCT. These tumors also had higher expression levels of CD19 and CD81.

CONCLUSIONS

PFS analyses suggest that lenalidomide and ixazomib target tumors with different levels of c-MYC, CD19, and CD81 expression, thus providing a potential rationale for the differential benefits observed in the TOURMALINE-MM1 study. This trial was registered at www.clinicaltrials.gov as: NCT01564537.

Relapsed refractory multiple myeloma: a comprehensive overview

Most patients with relapsed/refractory multiple myeloma (RRMM) have been treated with drug combinations including a proteasome inhibitor (PI) and/or an immunomodulatory drug (IMiD). The goal of therapy for such patients is therefore to achieve disease control with acceptable toxicity and patient-defined decent quality of life. Physicians face a difficult task not only deciding who to treat, but also when to treat and how to treat, utilizing knowledge of previously administered therapies, patient comorbidities, potential adverse events, and patient wishes to make such a critical decision. New drugs and combination regimens are continuously underway thus broadening the options for therapy and giving way to a more individualized approach for patients with RRMM. The integration of novel agents into the treatment paradigm has shifted the perception of multiple myeloma (MM) from an incurable, fatal disease to a manageable, chronic one. This comprehensive review addresses the results and challenges posed by many of the newer agents for the treatment of RRMM. It attempts to propose a universal strategy for optimal therapy decision-making thus answering three simple fundamental questions-when to treat, how to treat, and how long to treat for.

Pomalidomide-dexamethasone for treatment of soft-tissue plasmacytomas in patients with relapsed / refractory multiple myeloma

OBJECTIVE

The presence of plasmacytomas (Ps) in patients with multiple myeloma (MM) is associated with a poor outcome, both in patients treated conventionally and in patients treated with novel agents. Two types of plasmacytomas have being recognized: paraskeletal plasmacytomas (PPs) and extramedullary plasmacytomas (EMPs), being the incidence of EMPs lower but with worse prognosis. Our aim has been to analyze the efficacy of the pomalidomide-dexamethasone combination in this patient profile.

METHOD

In the present study, the efficacy of pomalidomide and dexamethasone in 21 patients from nine hospitals of Catalonia (Spain), with relapsed or refractory MM and Ps, was analyzed. For this purpose, we describe the evolution of paraprotein in serum and urine and the size of plasmacytomas during treatment with pomalidomide-dexamethasone.

RESULTS

While 34% of the patients achieved a paraprotein response, only two patients with PPs (9%) responded (RC and PR). There were no responses among patients with EMPs. The median progression-free survival from the start of treatment with pomalidomide/dexamethasone was only 1.7 months and the median overall survival of 4.5 months.

CONCLUSION

In conclusion, pomalidomide and dexamethasone has limited efficacy in patients with advanced MM and soft-tissue plasmacytomas.

Treatment of Relapsed Myeloma in a Patient With Renal Insufficiency

The Oncology Grand Rounds series is designed to place original reports published in the Journal into clinical context. A case presentation is followed by a description of diagnostic and management challenges, a review of the relevant literature, and a summary of the authors' suggested management approaches. The goal of this series is to help readers better understand how to apply the results of key studies, including those published in Journal of Clinical Oncology, to patients seen in their own clinical practice. A 45-year-old man was diagnosed in March 2010 with stage III immunoglobulin G kappa multiple myeloma (MM) after presenting with bone pain as a result of multiple lytic bone lesions and T12 vertebral collapse. Laboratory work-up showed a serum M protein of 72 g/L and a 24-hour kappa light-chain urine protein excretion of 730 mg, hemoglobin of 10.2 g/dL, serum albumin of 49 g/L, serum β₂-microglobulin of 6.4 mg/L, serum creatinine level of 1.6 mg/dL with an estimated glomerular filtration rate (eGFR) of 47 mL/min/1.73 m², and normal serum calcium and lactate dehydrogenase (LDH) levels. His bone marrow contained 58% plasma cells, which showed the 17p deletion abnormality (Fig 1). He was treated with vertebroplasty and alternating chemotherapy with carmustine, vincristine, cyclophosphamide, melphalan, and prednisone and vincristine, carmustine, doxorubicin and dexamethasone. Because of progressive disease, salvage therapy with bortezomib and dexamethasone was administered with no response. The patient was then switched to lenalidomide and dexamethasone, which yielded minimal response. He underwent autologous stem-cell transplantation (ASCT) with melphalan 200 mg/m² as high-dose therapy in February 2011, which led to a partial response, but in December 2011, progressive disease was documented, and the patient was enrolled in a clinical trial of carfilzomib monotherapy, with stable disease for 33 cycles. In October 2014 serum M protein rose to 38.6 g/L, with 24-hour kappa light-chain urine protein excretion of 840 mg, serum creatinine of 2.1 mg/dL, and an eGFR of 41 mL/min/1.73 m². He presented to discuss ongoing treatment options.

Myeloid transformation of plasma cell myeloma: molecular evidence of clonal evolution revealed by next generation sequencing

Background

Plasma cell myeloma (PCM) is a neoplasm of terminally differentiated B lymphocytes with molecular heterogeneity. Although therapy-related myeloid neoplasms are common in plasma cell myeloma patients after chemotherapy, transdifferentiation of plasma cell myeloma into myeloid neoplasms has not been reported in literature. Here we report a very rare case of myeloid neoplasm transformed from plasma cell myeloma.

Case presentation

A 60-year-old man with a history of plasma cell myeloma with IGH-MAF gene rearrangement and RAS/RAF mutations developed multiple soft tissue lesions one year following melphalan-based chemotherapy and autologous stem cell transplant. Morphological and immunohistochemical characterization of the extramedullary disease demonstrated that the tumor cells were derived from the monocyte-macrophage lineage. Next generation sequencing (NGS) studies detected similar clonal aberrations in the diagnostic plasma cell population and post-therapy neoplastic cells, including IGH-MAF rearrangement, multiple genetic mutations in RAS signaling pathway proteins, and loss of tumor suppressor genes. Molecular genetic analysis also revealed unique genomic alterations in the transformed tumor cells, including gain of NF1 and loss of TRAF3.

Conclusion

To our knowledge, this is the first case of myeloid sarcoma transdifferentiated from plasma cell neoplasm. Our findings in this unique case suggest clonal evolution of plasma cell myeloma to myeloma neoplasm and the potential roles of abnormal RAS/RAF signaling pathway in lineage switch or transdifferentiation.

Recovery of polyclonal immunoglobulins one year after autologous stem cell transplantation as a long-term predictor marker of progression and survival in multiple myeloma

Immunoparesis or suppression of polyclonal immunoglobulins is a very common condition in newly diagnosed myeloma patients. However, the recovery of polyclonal immunoglobulins in the setting of immune reconstitution after autologous stem cell transplantation and its effect on outcome has not yet been explored. We conducted this study in a cohort of 295 patients who had undergone autologous transplantation. In order to explore the potential role of immunoglubulin recovery as a dynamic predictor of progression or survival after transplantation, conditional probabilities of progression-free survival and overall survival were estimated according to immunoglobulin recovery at different time points using a landmark approach. One year after transplant, when B-cell reconstitution is expected to be completed, among 169 patients alive and progression free, 88 patients (52%) showed immunoglobulin recovery and 81 (48%) did not. Interestingly, the group with immunoglobulin recovery had a significantly longer median progression-free survival than the group with persistent immunoparesis (median 60.4 vs. 27.9 months, respectively; Hazard Ratio: 0.45, 95%Confidence Interval: 0.31-0.66; P<0.001), and improved overall survival (11.3 vs. 7.3 years; Hazard Ratio: 0.45, 95%Confidence Interval: 0.27-0.74; P=0.002). Furthermore, the percentage of normal plasma cells detected by flow cytometry in the bone marrow assessed at day 100 after transplantation was associated with the immunoglobulin recovery at that time and may predict immunoglobulin recovery in the subsequent months: nine months and one year. In conclusion, the recovery of polyclonal immunoglobulins one year after autologous transplantation in myeloma patients is an independent long-term predictor marker for progression and survival.

Absence of spontaneous response improvement beyond day +100 after autologous stem cell transplantation in multiple myeloma

The response evaluation after autologous stem-cell transplantation (ASCT) is usually performed at day +100 in patients with multiple myeloma (MM). A recent report suggests that improvement in the response can be observed beyond day +100. The aim of the present study has been to evaluate the rate of improved response and outcome beyond day +100 after ASCT, with and without maintenance therapy. One hundred and forty-four patients who underwent single ASCT with chemosensitive disease and achieved less than CR at day 100 post ASCT were evaluated. Seventy-four patients (51.4%) did not receive any maintenance with only one of them showing an upgrade in the response. The remaining 70 patients (48.6%) received maintenance therapy; eleven of them (15.7%) improved their response beyond day +100. The outcome of these patients was better than those who did not upgrade their response in both progression-free survival and overall survival (P=0.019 and P=0.031, respectively). In conclusion, the improvement in response beyond day +100 after ASCT in patients not receiving any therapy is exceedingly rare. A minority of patients receiving maintenance therapy after ASCT upgrades their response and this finding is associated with better outcome.

The possible role of burden of therapy on the risk of myeloma extramedullary spread

Extramedullary relapse (EMR) represents a poor prognostic marker in the course of multiple myeloma (MM). We reviewed data from 329 patients, diagnosed between 2000 and 2010, without extramedullary disease at onset to explore possible risk factors for EMR. The median overall survival of our study cohort was 6.4 years. The risk of EMR was 28 % with a median time from diagnosis to first EMR of 2.2 years (0.2-9.1 years). Patients with soft tissue masses located in extra-osseous organs (EMR-S) showed the worst outcome, compared to those with tumor masses arising from adjacent bone (EMR-B) (median OS 1.6 vs 2.4 years, p = 0.006). In addition, patients with EMR-S showed a significant trend for further development of extramedullary masses in a very short time (3.7 vs 5.7 months for EMR-B, p = 0.043). Multivariate analysis failed to identify any clinically presenting features predictive for EMR. The occurrence of EMR was higher in patients with more complex treatment history, defined on the basis of longer treatment duration (≥6 vs <6 months) and on elevated number of treatment lines administered (>2 vs ≤2 lines) (HR = 4.5, p < 0.001 and HR = 9.0, p < 0.001, respectively, when one or both factors are present).In conclusion, increasing burden of treatment might be a possible risk factor for EMR. MM patients with multiple relapses should be comprehensively investigated including, when possible, a whole-body-targeted radiologic technique to accurately detect EMR. Treatment choice should take into account the very poor outcome for patients with soft tissue involvement.

Treatment of relapsed and refractory multiple myeloma

The approach to the patient with relapsed or relapsed/refractory multiple myeloma (RRMM) requires a careful evaluation of the results of previous treatments, the toxicities associated with them and an assessment of prognostic factors. Since the majority of patients will have received prior therapy with drug combinations including a proteasome inhibitor and/or an immunomodulatory drug (IMiD), it is the physician's task to choose the right moment for the start of therapy and define with the patient which goals need to be achieved. The choice of regimen is usually based on prior responsiveness, drugs already received, prior adverse effects, the condition of the patient and expected effectiveness and tolerability. Many double and triple drug combinations are available. In addition, promising new drugs like pomalidomide, carfilzomib and monoclonal antibodies are, or will be, available shortly, while other options can be tried in clinical studies. Finally, supportive care and palliative options need to be considered in some patients. It is becoming increasingly more important to consider the therapeutic options for the whole duration of the disease rather than take a step by step approach, and to develop a systematic approach for each individual patient.

Zoledronic acid as compared with observation in multiple myeloma patients at biochemical relapse: results of the randomized AZABACHE Spanish trial

This study analyzed the anti-myeloma effect of zoledronic acid monotherapy by investigating patients at the time of asymptomatic biochemical relapse. One hundred patients were randomized to receive either zoledronic acid (4 mg iv/4 weeks, 12 doses) (n=51) or not (n=49). Experimental and control groups were well balanced for disease and prognostic features. Zoledronic acid did not show an antitumor effect according to changes in M-component. However, there were fewer symptomatic progressions in the experimental group than in the control group (34 versus 41, respectively; P=0.05) resulting in a median time to symptoms of 16 versus 10 months (P=0.161). The median time to next therapy was also slightly longer for the treated group than the untreated, control group (13.4 versus 10.1 months), although the difference was not statistically significant (P=0.360). The pattern of relapses was different for treated versus control patients: progressive bone disease (8 versus 20), anemia (24 versus 18), renal dysfunction (1 versus 2), and plasmacytomas (1 versus 1, respectively). This concurred with fewer skeletal-related events in the treated group than in the control group (2 versus 14), with a projected 4-year event proportion of 6% versus 40% (P<0.001). In summary, zoledronic acid monotherapy does not show an antitumor effect on biochemical relapses in multiple myeloma, but does reduce the risk of progression with symptomatic bone disease and skeletal complications. This trial was registered in the ClinicalTrials.gov database with code NCT01087008.

How I treat relapsed myeloma

Multiple myeloma (MM) is a plasma cell malignancy leading to significant life-expectancy shortening. Although the incorporation of the novel agents thalidomide, bortezomib, and lenalidomide in the front-line therapy has resulted in significant improvement, almost all patients relapse, making the treatment of relapse a real challenge. In the present article, when and how to treat relapsed MM is discussed. Treatment can be safely delayed in a subset of patients with asymptomatic relapse, whereas those with symptomatic relapse, advanced disease at diagnosis, or significant paraproteinemic increase require prompt rescue therapy. The benefit of retreatment and the use of a sequential approach for successive relapses considering drug synergism are highlighted. For patients with aggressive relapses and for those who have exhausted all available options, continued therapy until disease progression is recommended, particularly when using regimens with a long-term safety profile. Patients with a duration response to a first autologous stem cell transplantation (ASCT) longer than 2 years may benefit from a second ASCT. Patients with aggressive disease and/or poor cytogenetics at diagnosis relapsing within the first 2 years from ASCT should be considered for an allogeneic transplantation. Finally, a number of newer promising drugs are being actively investigated and the enrolment of patients in clinical trials is encouraged.

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.

The glutathione synthesis inhibitor buthionine sulfoximine synergistically enhanced melphalan activity against preclinical models of multiple myeloma

Melphalan (L-PAM) has been an integral part of multiple myeloma (MM) treatment as a conditioning regimen before stem cell transplant (SCT). After initial response, most treated patients experience relapse with an aggressive phenotype. Increased glutathione (GSH) in MM may mediate resistance to L-PAM. We demonstrated that the GSH synthesis inhibitor buthionine sulfoximine (BSO) synergistically enhanced L-PAM activity (inducing 2–4 logs of cell kill) against nine MM cell lines (also in the presence of marrow stroma or cytokines) and in seven primary MM samples (combination indices <1.0). In MM cell lines, BSO significantly (P<0.05) depleted GSH, increased L-PAM-induced single-strand DNA breaks, mitochondrial depolarization, caspase cleavage and apoptosis. L-PAM depleted GSH, but GSH rapidly recovered in a L-PAM-resistant MM cell line unless also treated with BSO. Treatment with N-acetylcysteine antagonized BSO+L-PAM cytotoxicity without increasing GSH. In human MM xenografted into beige-nude-xid mice, BSO significantly depleted MM intracellular GSH and significantly increased apoptosis compared with L-PAM alone. BSO+L-PAM achieved complete responses (CRs) in three MM xenograft models including maintained CRs >100 days, and significantly increased the median event-free survival relative to L-PAM alone. Combining BSO with L-PAM warrants clinical testing in advanced MM.