Carfilzomib, Lenalidomide, and Dexamethasone in High-Risk Smoldering Multiple Myeloma: Final Results from the NCI Phase 2 Pilot Study

BACKGROUND: Early treatment with lenalidomide and dexamethasone delays progression and increases overall survival in patients with high-risk smoldering multiple myeloma. The addition of the selective proteasome inhibitor carfilzomib to a lenalidomide and dexamethasone backbone has proven effective in patients with newly-diagnosed multiple myeloma; this combination may allow patients with high-risk smoldering multiple myeloma to obtain deep and durable responses. METHODS: In this phase 2 pilot study, patients with high-risk smoldering multiple myeloma received eight 28-day cycles of induction therapy with carfilzomib (at a dose of 20/36 mg per square meter on days 1, 2, 8, 9, 15, and 16), lenalidomide (at a dose of 25 mg on days 1–21), and dexamethasone (at a dose of 10 or 20 mg on days 1, 2, 8, 9, 15, 16, 22, and 23). Patients achieving stable disease or better after combination therapy received 2 years of maintenance therapy with lenalidomide. Minimal residual disease was assessed with multi-color flow cytometry, next-generation sequencing by the LymphoSIGHT method, and fluorodeoxyglucose-positron emission tomography-computed tomography (FDG-PET/CT). Myeloma clonotypes were identified in genomic DNA obtained from CD138+ bone marrow cell lysate or cell-free bone marrow aspirate at baseline for each patient based on their high frequency within the B-cell repertoire. Per study protocol, minimal residual disease assessment by next-generation sequencing, multi-color flow cytometry and FDG-PET/CT was repeated when patients achieved a complete response or completed 8 cycles of induction treatment. A sample size of 12 evaluable patients was calculated as being minimally necessary based on the following probability calculations: If the true probability of a very good partial response was 20% or 50%, we calculated that there would be a 7.3% or 80.6% probability, respectively, if 5 or more patients exhibiting a very good partial response (VGPR). Thus, if 5 or more patients out of 12 achieved a very good partial response, there would be strong evidence that the true probability of a VGPR was 50% or more. RESULTS: Twelve patients were enrolled. All 11 patients (100%) who completed 8 cycles of combination therapy obtained VGPR or better (primary end point). Minimal residual disease assessment by next-generation sequencing was performed on bone marrow supernatant to detect cell-free myeloma clonotypes, while flow cytometry analysis utilized bone marrow cells. Overall (N=12), 100% of patients achieved a complete response or better over the study period, including 11 patients (92%) negative for minimal residual disease based on multi-color flow cytometry. Based on next-generation sequencing, two of the 12 patients were positive for minimal residual disease in the bone marrow supernatant; one of these two patients was also positive for minimal residual disease based on multi-color flow cytometry in the bone marrow cells. Information regarding longitudinal minimal residual disease status will be available and presented at the meeting. Adverse events were manageable. CONCLUSIONS: Early treatment with carfilzomib, lenalidomide, and dexamethasone was associated with high rates of complete response and minimal residual disease negativity by multi-color flow cytometry, next-generation sequencing, and FDG-PET/CT in patients with high-risk smoldering multiple myeloma. Disclosures Landgren: Onyx Pharmaceuticals: Consultancy; Medscape: Consultancy; Millennium Pharmaceuticals: Independent Data Monitoring Committee (IDMC), Independent Data Monitoring Committee (IDMC) Other. Off Label Use: Carfilzomib and lenalidomide for high-risk smoldering multiple myeloma.