Sustained High Rates of Complete Response and Minimal Residual Disease Negativity after 8 Cycles of Carfilzomib (CFZ), Lenalidomide (LEN), and Dexamethasone (DEX) Followed By 2 Years of Lenalidomide Maintenance (CRd-R) in Patients with High-Risk Smoldering Multiple Myeloma: Updated Results of Clinical and Correlative Phase 2 Study

Background: High-risk smoldering multiple myeloma (HR-SMM) is a plasma cell dyscrasia which has a 5-year risk of progression to symptomatic multiple myeloma (MM) of approximately 75% based on current risk models. With the availability of novel therapies, early treatment may decrease the risk of progression and prolong survival as evidenced by the recent QuiRedex study results. More recently, studies have demonstrated that triplet regimens are superior to doublet in MM and whole exome sequencing in HR-SMM is indicative of treatment susceptible biology in early disease; supporting the use of effective combination therapy as early intervention. Expanding on our initial results using modern CRd-R therapy in HR-SMM patients (Korde et al. JAMA Onc 2015) we show unprecedented high rates of obtained and sustained complete response (CR) and minimal residual disease negativity (MRDneg CR) in an expanded cohort of patients with a median follow-up of ~3 years. Methods: Treatment-na•ve patients with HR-SMM (IMWG 2010 criteria; Mayo or PETHEMA models) were treated for 8 cycles (28-day cycles) with CFZ 20/36 mg/m2 IV days 1, 2, 8, 9, 15, 16; LEN 25 mg PO days 1-21, and DEX 20/10 mg IV/PO days 1, 2, 8, 9, 15, 16, 22, 23. Transplant eligible patients underwent stem cell collection after ≥4 cycles of CRd and then continued CRd treatment (i.e. by-default-delayed high-dose melphalan with autologous stem cell transplant; HDM-ASCT). After 8 cycles of combination therapy, patients with SD or better received 2 years of LEN 10 mg PO maintenance. The primary objective was best response (ORR), followed by secondary objectives of progression free survival (PFS) and response duration (DoR) which were assessed after every cycle of induction and every 90 days during maintenance. Correlative studies including assessment of minimal residual disease (MRD) by multi-color flow cytometry (bone marrow aspirate; 10-5 sensitivity) as defined by updated 2016 IMWG response criteria were performed after 8 cycles of induction and 1 and 2 years of maintenance LEN. Results: Eighteen patients meeting eligibility criteria were enrolled (data-lock 7/20/2016). Demographics and disease characteristics are shown in Table 1. Best ORR and >= VGPR rate (n=18) with CRd-R was 100% (Table 2). The proportion of patients who obtained stringent CR/CR after 8 cycles of induction, 1 year of maintenance and 2 years of maintenance was 61%, 89%, and 89%, respectively. Of evaluable patients who achieved at least a CR, the proportion of patients who obtained MRD negativity (MRDneg CR) at the same time-points was 91%, 71%, and 75%, respectively. DoR and PFS at 36 months was 94% and overall survival with a median follow-up duration of 31 months was 100%. Toxicities Grade 3-4 occurring in >1 patient included lymphopenia (39%), neutropenia (28%), anemia (22%), diarrhea (17%), lung infection (17%), hypophosphatemia (11%), and thromboembolic event (11%). Significant serious adverse events included CHF which occurred in one patient. Conclusions: Early treatment of HR-SMM with modern CRd-R combination therapy with by-default-delayed HDM-ASCT resulted in unprecedented high rates of CR and MRDneg CR after 8 cycles of CRd. Following 2 years of additional LEN maintenance therapy, the CR and sustained MRDneg CR rates were 89% and 69%, respectively. Given the significant risk of progression to symptomatic MM and associated life limiting end-organ damage, early intervention for patients with HR-SMM with effective triplet-based therapies may be warranted. This first proof-of-principle study has thus far demonstrated exceptional clinical benefit. Therefore, this study will be re-opened to enrollment and long-term follow up results collected to expand on these promising results. Updated results will be presented at the Annual Meeting. Disclosures Korde: Medscape: Honoraria. Bhutani:Prothena: Research Funding; Takeda Oncology: Research Funding, Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Onyx, an Amgen subsidiary: Speakers Bureau. Landgren:BMS: Honoraria; Amgen: Honoraria, Research Funding; Novartis: Honoraria; Celgene: Honoraria, Research Funding; Takeda: Honoraria.