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8001 Background: Patients with ultra high-risk (UHiR) newly diagnosed multiple myeloma (NDMM) and patients with plasma cell leukemia (PCL) continue to have dismal outcomes and are underrepresented in clinical trials. Recently, improved responses with anti-CD38 monoclonal antibody combination therapy have been reported for NDMM patients. We report here outcomes for NDMM UHiR and PCL patients treated in the OPTIMUM/MUKnine (NCT03188172) trial with daratumumab, cyclophosphamide, bortezomib, lenalidomide, dexamethasone (Dara-CVRd) induction, augmented high-dose melphalan (HDMEL) and ASCT. With final analysis follow-up surpassed in Feb 2021, we report here early protocol defined endpoints from induction to day 100 post ASCT. Methods: Between Sep 2017 and Jul 2019, 107 patients with UHiR NDMM by central trial genetic (≥2 high risk lesions: t(4;14), t(14;16), t(14;20), gain(1q), del(1p), del(17p)) or gene expression SKY92 (SkylineDx) profiling, or with PCL (circulating plasmablasts > 20%) were included in OPTIMUM across 39 UK hospitals. Patients received up to 6 cycles of Dara-CVRd induction, HDMEL and ASCT augmented with bortezomib, followed by Dara-VR(d) consolidation for 18 cycles and Dara-R maintenance. Primary trial endpoints are minimal residual disease (MRD) status post ASCT and progression-free survival. Secondary endpoints include response, safety and quality of life. Data is complete but subject to further data cleaning prior to conference. Results: Median follow-up for the 107 patients in the safety population was 22.2 months (95% CI: 20.6 – 23.9). Two patients died during induction due to infection. Bone marrow aspirates suitable for MRD assessment by flow cytometry (10-5 sensitivity) were available for 81% of patients at end of induction and 78% at D100 post ASCT. Responses in the intention to treat population at end of induction were 94% ORR with 22% CR, 58% VGPR, 15% PR, 1% PD, 5% timepoint not reached (TNR; withdrew, became ineligible or died) and at D100 post ASCT 83% ORR with 47% CR, 32% VGPR, 5% PR, 7% PD, 10% TNR. MRD status was 41% MRDneg, 40% MRDpos and 19% not evaluable post induction and 64% MRDneg, 14% MRDpos and 22% not evaluable at D100 post ASCT. Responses at D100 post ASCT were lower in PCL with 22% CR, 22% VGPR, 22% PR, 22% PD, 12% TNR. Most frequent grade 3/4 AEs during induction were neutropenia (21%), thrombocytopenia (12%) and infection (12%). Grade 3 neuropathy rate was 3.7%. Conclusions: This is to our knowledge the first report on a trial for UHiR NDMM and PCL investigating Dara-CVRd induction and augmented ASCT. Response rates were high in this difficult-to-treat patient population, with toxicity comparable to other induction regimens. However, some early progressions highlight the need for innovative approaches to UHiR NDMM. Clinical trial information: NCT03188172.

8009 Background: Immunomodulatory (IMiD) agents are effective therapies for multiple myeloma (MM), with Lenalidomide (Len) having fewer side effects than Thalidomide (Thal), enabling long-term treatment. The optimum IMiD induction and maintenance regimen are unknown. We therefore compared triplet induction regimens of Len vs Thal and examined the role of maintenance Len vs observation, enabling us to explore the interaction of Len induction with Len maintenance. Methods: Myeloma XI is a multicenter, randomized controlled trial for newly diagnosed MM, with pathways for transplant eligible (TE) and non-eligible patients. For TE patients the induction question compared Len or Thal plus cyclophosphamide and dexamethasone (CRD vs CTD) continued for a minimum of 4 cycles and to max. response. For patients with a suboptimal response there was a subsequent randomization to a proteasome inhibitor containing triplet or no further therapy prior to ASCT. A maintenance randomization at 3 months post ASCT compared Len till disease progression vs observation. 2042 TE patients underwent the induction randomization (CRD 1021, CTD 1021). After a median follow up of 36.3 months, 965 PFS and 415 OS primary endpoint events had occurred. Secondary endpoints included response and toxicity. Results: In TE patients, CRD induction was associated with deeper responses than CTD: ≥VGPR CRD 60% vs CTD 53%. This was associated with a significantly improved median PFS (HR 0.85, 95%CI 0.75, 0.96, CRD 35.9 months vs CTD 32.9, p=0.0116) and 3 year OS: 82.9% vs 77.0% (HR 0.77, 95%CI 0.63, 0.93, p=0.0072). Maintenance therapy with Len was associated with a significantly longer median PFS compared to observation (HR 0.47, 95%CI 0.38, 0.60) across all subgroups including patients with high-risk disease. Exploratory analysis across the TE pathway suggested that CRD induction with Len maintenance was optimum: 60 month PFS CRD-R 50.2%, CTD-R 39.1%, CRD-obs 18.5%, CTD-obs 23.4%. Conclusions: CRD was associated with deeper responses than CTD, and with a PFS and OS benefit. The best outcomes were associated with Len induction plus Len maintenance. Our findings support continuing Len therapy through induction until disease progression. Clinical trial information: NCT01554852.