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Introduction As lenalidomide (Len) has become an integral part of therapy for newly diagnosed MM patients, most will have been either exposed or refractory to Len at the time of first or second relapse. The monoclonal antibody, Daratumumab, in combination with the more potent IMID pomalidomide (Pom) demonstrates good responses in patients previously exposed to lenalidomide. Low dose weekly cyclophosphamide has been shown to enhance the potency of pomalidomide in association with dexamethasone. In this clinical trial, we set out to compare the combination of daratumumab, weekly low dose cyclophosphamide, dexamethasone and pomalidomide (DCdP) to daratumumab, cyclophosphamide and dexamethasone (DCd) with pomalidomide added only at disease progression. Although we expected that a four-drug regiment would give superior clinical results, we hypothesized that a significant number of patients would not necessarily need all four drugs but could benefit from the addition of pomalidomide at treatment failure. Patients/Methods In this phase II clinical trial 120 patients with relapsed refractory myeloma, after at least one line of therapy, were randomized to receive either daratumumab (16mg/kg) weekly IV C1-2, every 2 weeks C3-6, monthly C7+, dexamethasone 40mg po weekly, cyclophosphamide 400mg po weekly and pomalidomide 4mg po days 1-21 of 28 day cycles (Arm A) or the same doses and dosing regimen of daratumumab, cyclophosphamide and dexamethasone but with pomalidomide added only after confirmed disease progression (Arm B). All patients had to be exposed to proteasome inhibitors and len prior to study entry. The primary endpoint of this study is the comparison of the PFS of Arm A and the PFS of Arm B after the addition Pom (PFS2) at 36 months while secondary endpoints included overall responses, duration of responses, survival and safety. Correlative laboratory studies are also planned. Results As of 1 April 2019 all 120 patients have been enrolled in 11 sites across Canada. The patient characteristics were: median age 65 (range 39-82); median 2 prior lines of therapy (range 1-8); 70% had a previous ASCT; 95% lenalidomide exposed; 93% proteasome inhibitor exposed; 90% lenalidomide and PI exposed; 25% carfilzomib exposed, len was the last line of therapy in 65%. Median follow-up was 8.2 months (range 1-15.6), median number of cycles 8 (range 1-17). The overall response rates (ORR) were 88.5% for arm A compared with 50.8% for arm B, with 57.4% and 25.4% of patients achieving ≥VGPR in arm A and B respectively. Among the 20 patients in Arm B that had progressed by data cutoff, the ORR after adding pomalidomide was 40% albeit with the short follow up time of 3.4 months. Although the median PFS of Arm A has not yet been reached, it was 10.9 mo. in Arm B prior to the addition of pom and 14.3 mo. from trial entry in the smaller group in whom pom was added after first progression (PFS2). In Arm A the 9- month PFS was 83%. Rates of grade 3/4 hematologic toxicities included a high incidence of neutropenia, 74% in Arm A and 30% in Arm B; however the rates of febrile neutropenia were low at 8.2% and 6.8% respectively. Grade 3/4 thrombocytopenia were 4.9% and 13.6%, respectively. The most common non-hematologic toxicity was pneumonia in 18% and 16.9% in arms A and B, respectively. Conclusions The results of this randomized phase II trial demonstrate that in a moderately pretreated MM population (median 2 lines of therapy but range 1-8) that the four-drug combination (DCdP) confers impressive response rates (ORR 88.5%) and a 9-month PFS of 83%. Although the three-drug combination (DCd) showed an inferior response rate of 50%, this is superior to Daratumumab used as a single agent in a similar patient population and so far at least 40% of patients who have progressed appear salvageable showing responses upon addition of Pom. Moreover, the addition of low dose cyclophosphamide, an alkylator with recognized immune properties, appears to enhance ORR and produce a durable PFS even when compared to Dara-pom-dex combinations used after two lines of therapy. Toxicities were principally hematologic and few resulted in treatment discontinuations. Disclosures Sebag: Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Bahlis:Amgen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria. Venner:Celgene: Research Funding; Amgen: Honoraria, Research Funding; Janssen: Honoraria; Takeda: Honoraria. McCurdy:Celgene: Honoraria; Janssen: Honoraria. Shustik:Takeda: Honoraria; Amgen: Honoraria; Janssen: Honoraria; Celgene: Honoraria. White:Sanofi: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria. Kotb:Karyopharm: Equity Ownership; Amgen: Honoraria; Merck: Honoraria, Research Funding; Celgene: Honoraria; Janssen: Honoraria; Takeda: Honoraria. Stakiw:Roche: Research Funding; Lundbeck: Honoraria; BMS: Honoraria; Novartis: Honoraria, Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Janssen: Honoraria, Research Funding, Speakers Bureau; Sanofi: Honoraria. Laferriere:Celgene: Honoraria; Taiho: Honoraria; Teva Pharm: Honoraria; ROCHE: Honoraria; Pfizer: Honoraria; Janssen: Honoraria; Takeda: Honoraria; Novartis: Honoraria; Astra Zeneca: Honoraria; Amgen: Honoraria. Camacho:Abbvie: Consultancy; Janssen: Consultancy; Baush-Health: Consultancy. Reece:Otsuka: Research Funding; BMS: Research Funding; Merck: Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Honoraria, Research Funding.

Introduction: Daratumumab, a human IgGκ monoclonal antibody targeting CD38 with a direct on-tumor and immunomodulatory mechanism of action, is approved in combination with standard-of-care regimens for the treatment of newly diagnosed multiple myeloma (NDMM) and RRMM. When combined with standard of care regimens across four phase 3 studies, daratumumab demonstrated ≥44% reductions in the risk of progression or death, nearly doubled complete response (CR) or better rates, and tripled minimal residual disease (MRD)-negative rates at the 10-5 sensitivity threshold in pts with RRMM or NDMM (Palumbo A, et al. N Engl J Med 2016. 375[8]:754-766; Dimopoulos MA, et al. N Engl J Med 2016. 375[14]:1319-1331; Mateos MV, et al. N Engl J Med 2018. 378[6]:518-528; Facon T, et al. N Engl J Med 2019. 380[22]2104-2015). In the phase 3 POLLUX study (median follow-up 44.3 months), D-Rd reduced the risk of disease progression or death by 56% and significantly increased the overall response rate (ORR) versus Rd alone (93% vs 76%; P 4 years of median follow-up. Methods: Pts who received ≥1 prior line of therapy were randomized (1:1) to Rd (lenalidomide 25 mg PO on Days 1-21 of each 28-day cycle; dexamethasone 40 mg per week) ± daratumumab (16 mg/kg IV QW for Cycles 1-2, Q2W for Cycles 3-6, then Q4W until disease progression). Cytogenetic risk was determined by local fluorescence in situ hybridization or karyotyping; pts with high cytogenetic risk had t(4;14), t(14;16), and del17p abnormalities. PFS on subsequent line of therapy (PFS2), an exploratory endpoint, was defined as time from randomization to progression after next line of subsequent therapy or death. Results: A total of 569 pts were randomized (D-Rd, n = 286; Rd, n = 283). At a median follow-up of 51.3 months, D-Rd significantly prolonged progression-free survival (PFS) versus Rd (median 45.8 vs 17.5 months; hazard ratio [HR], 0.43; 95% confidence interval [CI], 0.35-0.54; P The median duration of treatment was 34.3 months in the D-Rd arm versus 16.0 months in the Rd arm. The most common (≥10%) grade 3/4 treatment-emergent adverse events (TEAEs) observed with D-Rd versus Rd included neutropenia (56% vs 42%), anemia (18% vs 22%), thrombocytopenia (15% vs 16%), pneumonia (16% vs 10%), and diarrhea (10% vs 4%). Similar rates of discontinuations due to TEAEs were observed for D-Rd versus Rd (16% vs 15%). The incidence of invasive second primary malignancies was 4.9% and 5.7% for the D-Rd and Rd groups, respectively. Additional efficacy data, including minimal residual disease, and safety analyses will be presented at the meeting. Conclusion: After >4 years of median follow-up, D-Rd continues to demonstrate a significant PFS benefit and higher rates of deeper responses versus Rd alone in pts with RRMM. Although significant PFS benefit was observed with D-Rd in RRMM pts regardless of prior lines of therapy or cytogenetic risk status, the greatest benefit was observed when used in patients treated earlier with D-Rd. The significant improvement in PFS2 suggests a potential survival benefit, but OS data is still immature. No new safety concerns were identified with this additional follow-up. Disclosures Kaufman: Celgene: Consultancy; Winship Cancer Institute of Emory University: Employment; Takeda: Consultancy; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria; AbbVie: Consultancy; Bristol-Myers Squibb: Consultancy; Incyte: Consultancy; Karyopharm: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Consultancy; Amgen: Consultancy. Usmani:Amgen, Bristol-Myers Squibb, Celgene, Janssen, Merck, SkylineDX, Takeda: Other: Consultant/Advisor; Amgen, Celgene, Janssen, Sanofi, Takeda: Speakers Bureau; Amgen Array Biopharma, Bristol-Myers Squibb, Celgene, Janssen, Merck, Pharmacyclics, Sanofi, Takeda: Other: Research Grant. San-Miguel:Amgen, Bristol-Myers Squibb, Celgene, Janssen, MSD, Novartis, Roche, Sanofi, and Takeda: Consultancy, Honoraria. Bahlis:Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. White:Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria. Cook:Amgen, Bristol-Myers Squib, GlycoMimetics, Seattle Genetics, Sanofi: Honoraria; Janssen, Takeda, Sanofi, Karyopharm, Celgene: Consultancy, Honoraria, Speakers Bureau; Celgene, Janssen-Cilag, Takeda: Honoraria, Research Funding. Ho:Novartis: Other: Trial Investigator meeting travel costs; La Jolla: Other: Trial Investigator meeting travel costs; Janssen: Other: Trial Investigator meeting travel costs; Celgene: Other: Trial Investigator meeting travel costs. Moreau:Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria. Krevvata:Janssen: Employment. Pei:Janssen: Employment, Equity Ownership. Ukropec:Janssen: Employment, Equity Ownership. Renaud:Janssen: Employment, Equity Ownership. Trivedi:Janssen: Employment, Equity Ownership. Kobos:Janssen: Employment. Dimopoulos:Sanofi Oncology: Research Funding.