Introduction: MDS is associated with an erythroid maturation defect, characterized by ineffective erythropoiesis leading to anemia and RBC transfusion dependence. Treatment of anemia in lower-risk MDS remains an unmet medical need. Luspatercept is a first-in-class erythroid maturation agent which binds to select TGFβ superfamily ligands to reduce aberrant Smad2/3 signaling and enhance late-stage erythropoiesis (Suragani RN, et al. Nat Med. 2014;20:408-14). Preliminary clinical studies have shown promising activity in MDS (Platzbecker U, et al. Lancet Oncol. 2017;10:1338-47).

We report the results of a phase 3, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of luspatercept in patients with anemia due to Revised International Prognostic Scoring System (IPSS-R)-defined Very low-, Low-, or Intermediate-risk MDS with RS who require RBC transfusions. ClinicalTrials.gov identifier: NCT02631070.

Methods: Eligible patients were aged ≥ 18 years; had IPSS-R-defined Very low-, Low-, or Intermediate-risk MDS with RS according to the WHO 2016 criteria; were refractory, intolerant, or ineligible to receive erythropoiesis-stimulating agents (ESAs); and required RBC transfusions. Patients were randomized 2:1 to receive either luspatercept, at a starting dose level of 1.0 mg/kg with titration up to 1.75 mg/kg, if needed, or placebo, subcutaneously every 3 weeks for ≥ 24 weeks. The primary endpoint was RBC transfusion independence (RBC-TI) for ≥ 8 weeks between week 1 and week 24. A key secondary endpoint was RBC-TI for ≥ 12 weeks between week 1 and 24. Achievement of modified hematologic improvement-erythroid (mHI-E) response using IWG 2006 criteria was also assessed.

Results:^† A total of 229 patients were randomized and treated. Median age was 71 years (range 26-95), median time from diagnosis was 41.8 months (range 3-421), and 62.9% were male. Overall, patient baseline characteristics were balanced between the treatment groups. Patients received a median of 5 RBC units (range 1-20) transfused over 8 weeks during the 16 weeks prior to treatment (43.2% of patients had ≥ 6 RBC units/8 weeks, 27.9% had ≥ 4 to < 6 RBC units/8 weeks, and 28.8% had < 4 RBC units/8 weeks). At baseline, 138 (60.3%), 58 (25.3%), and 32 (14.0%) patients had serum erythropoietin levels < 200 IU/L, 200-500 IU/L, and > 500 IU/L, respectively. A total of 218 (95.2%) patients had previously received ESAs. Overall, 206 (90.0%) patients had an SF3B1 mutation.

Of 153 patients receiving luspatercept, 58 (37.9%) achieved the primary endpoint of RBC-TI for ≥ 8 weeks compared with 10 of 76 patients (13.2%) receiving placebo (odds ratio [OR] 5.1, P < 0.0001). Of those receiving luspatercept, 43 of 153 (28.1%) achieved the key secondary endpoint of RBC-TI for ≥ 12 weeks (weeks 1-24) compared with 6 of 76 (7.9%) receiving placebo (OR 5.1, P = 0.0002).

Patients receiving luspatercept were more likely to achieve an mHI-E response, defined as a reduction in transfusion of ≥ 4 RBC units/8 weeks or a mean hemoglobin increase of ≥ 1.5 g/dL/8 weeks in the absence of transfusions, compared with patients receiving placebo (52.9% vs 11.8% during weeks 1-24; P < 0.0001).

The safety profile of luspatercept was consistent with that reported in the phase 2 PACE-MDS study (Platzbecker U, et al. Lancet Oncol. 2017;10:1338-47).

Conclusions: Treatment with luspatercept resulted in a significantly reduced transfusion burden compared with placebo in patients with anemia due to IPSS-R-defined Very low-, Low-, or Intermediate-risk MDS with RS, who require RBC transfusions, and was generally well tolerated.

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