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Introduction: Belantamab mafodotin (belamaf; GSK2857916) is a B-cell maturation antigen (BCMA)-targeting antibody-drug conjugate. In the pivotal Phase II DREAMM-2 study, single-agent belamaf demonstrated deep and durable responses with a manageable safety profile in heavily pretreated patients with RRMM (Lonial et al. Lancet Oncol 2020). Responses were sustained at 13 months of follow-up; with belamaf (2.5 mg/kg administered intravenously [IV] every 3 weeks [Q3W]), overall response rate (ORR) was 32% and median duration of response (DoR) was 11.0 months (Lonial et al. ASCO 2020 Poster 436). Preclinical data suggest synergistic antimyeloma activity of belamaf in combination with pomalidomide/dexamethasone (Pd). Preliminary data from an ongoing Phase I/II study (NCT03715478) evaluating belamaf in combination with Pd (B-Pd) suggest an acceptable safety profile and early signs of clinical activity in patients with RRMM. The DREAMM-8 study (NCT04484623) will evaluate the efficacy and safety of B-Pd compared with pomalidomide, bortezomib, and dexamethasone (PVd). Methods: This Phase III, two-arm, randomized, open-label, multicenter study will include patients with measurable RRMM who have received ≥1 prior line of therapy (including lenalidomide), with documented disease progression during or after their most recent line of treatment. Patients aged ≥18 years with Eastern Cooperative Oncology Group Performance Status 0-2, adequate organ system function, and who provide informed consent will be eligible. Patients with prior exposure to BCMA-targeted therapies or pomalidomide and those intolerant/refractory to bortezomib will be excluded. Approximately 450 patients will be randomized (1:1) to Arm A (B-Pd) or Arm B (PVd), stratified by number of prior lines of treatment, prior exposure to bortezomib, and International Staging System status. No more than 50% of participants with two or more prior lines of treatment will be enrolled. In Arm A, patients will receive belamaf 2.5 mg/kg (IV) Q4W on Day 1 in Cycle 1 (28-day cycle) followed by belamaf 1.9 mg/kg (IV) Q4W on Day 1 in Cycle 2 onwards (28-day cycles); pomalidomide 4 mg (orally [PO]) will be administered on Days 1-21 and dexamethasone 40 mg (PO) on Days 1, 8, 15, and 22 in all cycles (28-day cycles). In Arm B, pomalidomide 4 mg (PO) will be administered Q3W on Days 1-14 in all cycles (21-day cycles); bortezomib 1.3 mg/m2 will be administered subcutaneously on Days 1, 4, 8, and 11 in Cycles 1-8, and Days 1 and 8 in Cycle 9+ (21-day cycles). Dexamethasone 20 mg (PO) will be administered on the day of and the day after bortezomib. The dose level of dexamethasone in each arm will be reduced by half in patients >75 years of age. Treatment in both arms will continue until progressive disease, unacceptable toxicity, withdrawal of consent, initiation of another anticancer therapy, or end of study or death. The primary endpoint is progression-free survival (PFS; time from randomization to the earliest date of documented disease progression or death [any cause]). Minimal residual disease negativity rate is a key secondary endpoint. Additional secondary endpoints include ORR, time to response, DoR, time to progression, overall survival, PFS2 (PFS after initiation of new anticancer therapy), safety, health-related quality of life, and pharmacokinetic and pharmacodynamic parameters. The study is planned to start in August 2020. Funding: GSK (Study 207499); drug linker technology licensed from Seattle Genetics; mAb produced using POTELLIGENT Technology licensed from BioWa. Disclosures Trudel: GSK, Celgene, Janssen, Amgen, Genentech: Research Funding; Celgene, Janssen, Takeda, Sanofi, Karyopharm, Amgen Canada: Honoraria; Celgene, Amgen, GSK: Consultancy, Research Funding. Davis:GSK: Current Employment, Current equity holder in publicly-traded company. Lewis:GSK: Current Employment, Current equity holder in publicly-traded company. Bakshi:GSK: Current Employment, Current equity holder in publicly-traded company. Chopra:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Montes de Oca:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Ferron-Brady:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Eliason:GSK: Current Employment, Current equity holder in publicly-traded company. Kremer:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company; Novartis: Current equity holder in publicly-traded company. Wu:GSK: Current Employment, Current equity holder in publicly-traded company.