Background: Magrolimab is a monoclonal antibody that blocks CD47, a “don’t eat me” signal overexpressed on cancer cells. CD47 blockade by magrolimab induces macrophage-mediated phagocytosis of tumor cells and is synergistic with azacitidine (AZA) via upregulation of “eat me” signals. Here we report final Phase 1b data in patients (pts) with untreated HR-MDS (NCT03248479). Methods: Pts with previously untreated intermediate-/high-/very high-risk MDS per IPSS-R received magrolimab IV as a priming dose (1 mg/kg) followed by ramp-up to a 30 mg/kg weekly or Q2W maintenance dose. AZA 75 mg/m² was administered IV or SC on Days 1–7 of each 28-day cycle. Primary endpoints were safety/tolerability and complete remission (CR) rate. Results: 95 pts (median age 69 years [range 28, 91]) were treated. IPSS-R risk was intermediate, high, or very high in 27%, 52%, and 21%, respectively. MDS was therapy-related in 22%; 26% (n=25) had a TP53 mutation and 62% had poor-risk cytogenetics (27% complex). Median (range) number of cycles was 6 (1, 27). The most common TEAEs included constipation (68%), thrombocytopenia (55%), anemia (52%), neutropenia (47%), nausea (46%), and diarrhea (44%). The most common Grade 3/4 TEAEs included anemia (47%), neutropenia (46%), thrombocytopenia (46%), and WBC count decreased (30%). 6 pts discontinued treatment due to AEs. 60-day mortality was 2%. Median Hb change from baseline (BL) at first post-dose sample was –0.7 g/dL (range –3.1, +2.4). CR and objective response (OR) rates were 33% and 75% with 31% of evaluable OR pts with abnormal cytogenetics at BL having cytogenetic CR. Median time to first OR, duration of CR (DCR), duration of OR, and PFS were 1.9, 11.1, 9.8, and 11.6 mos. OS rates at 12 and 24 mos were 75% and 52%, respectively (median NR with 17.1 mos follow-up for OS). For patients evaluated with sequential WES with a VAF cutoff of 5%, 3 of 3 pts with TP53 mutation who achieved CR had TP53 VAF <5% by C5D1. Favorable outcomes were observed in both TP53 mutant (40% CR, median OS 16.3 months) and wildtype pts (31% CR, median OS NR; Table). Conclusions: Magrolimab+AZA was well tolerated with promising efficacy in pts with untreated HR-MDS including those with TP53-mut and TP53-wt disease. A Phase 3 trial of magrolimab/placebo+AZA (ENHANCE: NCT04313881) is ongoing. Clinical trial information: NCT03248479.

*9 pts included in all pts had missing TP53 status. ^†Defined as CR+ PR + marrow CR + SD w/HI. HI, hematologic improvement; NR, not reached; SD, stable disease.