Two activin receptor fusion proteins show promise in anemia
Their white blood cell counts had to be under 13,000/μL, and they had to have no response, loss of response, or low chance of response to ESAs, reflected by serum erythropoietin of more than 500 mIU/mL.
Patients were a median age of 71, and 70% were male.
They received subcutaneous sotatercept at dose levels of 0.1, 0.3, 0.5, or 1.0 mg/kg once every 3 weeks for up to 24 months following the first treatment.
Sotatercept efficacy
The investigators evaluated efficacy for the entire cohort as well as in subgroups of patients with high transfusion burden (HTB) and low transfusion burden (LTB). Patients were defined as HTB if they required RBC transfusions of 4 or more units every 8 weeks and LTB as less than 4 units per 8 weeks.
Overall, 45% (24/53) of the evaluable patients achieved hematologic improvement as defined by IWG 2006 criteria.
Forty-two percent of HTB patients had a reduction in their transfusion burden of 4 or more RBC units per 8 weeks, with a median duration of longest response of 106 days (range, 62 to 345+). Eleven percent (5/44) achieved RBC transfusion independence of 56 days or more.
Sixty-three percent (5/8) of LTB patients achieved both RBC transfusion independence of 56 days or more and a mean hemoglobin increase of 1.5 mg/dL or more for at least 8 weeks.
Their maximum mean hemoglobin increase ranged from 1.9 to 4.4 g/dL, and the mean duration of RBC transfusion independence ranged from 76 to 233+ days. Of these 8 patients, 67% were in the 1.0 mg/kg cohort.
Sotatercept safety
“Most of the adverse events were not necessarily related to the treatment,” Dr Komrokji said, “and they were grade 1 or grade 2 toxicity.”
Twenty of 54* patients (37%) experienced 1 or more treatment-related adverse events, the most common of which were fatigue/asthenia (13%), headache (9%), decreased appetite (7%), nausea (7%), and dyspnea (6%).
Three patients discontinued the study due to treatment-emergent adverse events that were possibly related to sotatercept. One was for grade 2 hemolytic anemia, 1 for grade 3 hypertension, and 1 for grade 2 muscle weakness.
Dr Komrokji concluded saying the results showed “promising evidence of clinical activity” in these ESA-refractory, anemic, lower-risk MDS and CMML patients who have a “challenging and unmet need for treatment.”
He indicated that further exploration of sotatercept at higher dose levels and for longer treatment periods is planned and ongoing.
He presented the data as abstract 3251. The study was supported by Celgene Corporation. 
*One patient was excluded from the efficacy analysis due to a protocol violation.
