Background: The combination of daratumumab (Dara), pomalidomide (POM), and dexamethasone (dex) (DPd) has previously demonstrated deep and durable responses including high rates of minimal residual disease (MRD) negativity, in patients with relapsed/refractory (R/R) MM. Quadruplet regimens may further improve results. We report updated findings from a phase 2 multicenter trial of the addition of ixazomib to DPd (DIPd) in patients with early R/R MM. Methods: This is a prospective, multi-center, open-label, single arm phase II trial with a primary objective to evaluate the overall response rate (ORR), safety, and efficacy of DIPd. Secondary endpoints include progression-free survival (PFS), overall survival (OS), and MRD-negativity rate. A Simon’s optimal 2-stage design was used, with 14 subjects in stage 1 to assess response and 32 patients for stage 2. Eligible patients may not have had exposure Dara or ixazomib, may not have progressed on POM, and may have received ≥1 and ≤3 prior lines of therapy. The first six patients in the safety run-in received Dara 16mg/kg IV weekly x 8 doses, biweekly x 8 doses, then monthly, POM 4mg orally on days 1-21 of a 28-day cycle, ixazomib 4mg orally on days 1,8,15 every 28 days, and dex 20-40mg weekly. Grade 3-4 neutropenia was observed in 100% of patients, prompting dose reduction to ixazomib 3 mg and POM 3 mg by the DSMB. An amendment allowed subcutaneous Dara administration. MRD assessments are being performed by EuroFlow for patients in VGPR or suspected CR. Pharmacodynamic changes in patients’ tumor microenvironments were established by custom panel mass cytometry to include T-cell memory and activated subpopulations, B-cell content, NK-cell subpopulations as well as MDSCs, Tregs and T-exhaustive markers, monocytes and dendritic cells. Results: To date, 14 subjects have been treated in stage 1, and 18 patients in stage 2. Median age was 61.5 (range 41-87) years, 50% were female and 72% white. Median number of prior regimens was 1 (range 1-3), all patients were lenalidomide-exposed, and 47% (11/23) had high-risk cytogenetic features. The most common grade 3-4 treatment emergent adverse events included neutropenia (78%), infection (30%), leukopenia (11%), respiratory conditions (7%), psychiatric disturbance (4%), and thrombosis (4%). Median time on treatment was 4 months (1-29), with 11 patients remaining on DIPd and 5 deaths (4 due to progressive disease and 1 due to sepsis). ORR to date was 84% (16/19), and the best responses included: 5 (26%) sCR; 4 (21%) VGPR; 7 (37%) PR. After a median follow up of 12 months, the median OS was 39 months and PFS was 9.5 months. Conclusions: The quadruplet regimen DIPd is a well-tolerated combination that has shown early safety, efficacy, and ORR in early R/R myeloma, including patients with high-risk genetic abnormalities. Clinical trial information: NCT03590652.