Background: RRMM patients (pts) who fail lenalidomide (LEN) and bortezomib (BORT) have poor prognosis. High-risk cytogenetics predict shorter survival. POM + LoDEX has demonstrated efficacy in pts with prior LEN and BORT and high-risk cytogenetics. MM-003 is an open-label, multicenter, phase III trial comparing POM + LoDEX vs. HiDEX in RRMM pts who failed LEN and BORT treatment (Tx) and have progressed on their last therapy. Methods: Pts must have been refractory to the last prior Tx (progressive disease [PD] during or within 60 days) and failed LEN and BORT after ≥ 2 consecutive cycles of each (alone or in combination). Randomization was 2:1 to POM 4 mg D1–21 + DEX 40 mg (20 mg for pts aged > 75 y) weekly; or DEX 40 mg (20 mg for pts aged > 75 y) D1–4, 9–12, and 17–20 (28-day cycles). Tx continued until PD or unacceptable adverse events (AEs). The primary endpoint was progression-free survival (PFS). Secondary endpoints included OS and AEs. This analysis examined pts meeting modified high-risk cytogenetic criteria—del(17p13) and/or t(4p16/14q32). Results: 302 pts received POM + LoDEX, and 153 pts received HiDEX. 225 and 107 pts, respectively, were evaluable for cytogenetics. Baseline characteristics were similar. Median PFS and OS were significantly longer with POM + LoDEX vs. HiDEX, regardless of cytogenetic risk (Table). The most common grade 3/4 AEs were neutropenia, anemia, and infection (Table). Discontinuation due to AE was low: 4% vs. 6% (high risk) and 10% vs. 4% (standard risk). Conclusions: Median PFS and OS were significantly longer with POM + LoDEX vs. HiDEX in pts with cytogenetically-defined high-risk disease, consistent with results from the intent-to-treat population. Tolerability was acceptable. POM + LoDEX should be considered a new Tx option in pts failing LEN and BORT. Clinical trial information: NCT01311687.