Study of Sotatercept for the Treatment of Anemia in low-or Intermediate-1 Risk Myelodysplastic Syndromes (MDS) or Non-proliferative Chronic Myelomonocytic Leukemia (CMML)

Time to Erythroid Hematological Improvement (HI-E) Response

Time to first response = start date of first response (HI-E) - first dose date + 1 day. For NTDE participants (who required \< 4 units of RBCs in the 8 weeks prior to start of therapy), HI-E was defined as an increase of \>=1.5 g/dL hemoglobin sustained for 56 days over a period of \>=8 weeks. For TDE participants (who required \>=4 units of RBCs in the 8 weeks prior to start of therapy), HI-E was defined as a decrease of \>= 4 units of RBCs transfused sustained for 56 days over a period of 8 weeks.

Time frame: Day 1 to Day 87

Duration of Erythroid Hematological Improvement (HI-E)

The duration of HI-E response for participants who responded was (the last date of the consecutive hemoglobin \[Hgb\] measurements of the first \>=56 day interval) - (the first date of the consecutive Hgb measurements of the first \>=56 day interval) + 1 day.

Time frame: Day 1 to 183.7 weeks

Time to Progression to Acute Myeloid Leukemia (AML) for Participants Who Had Progression

Progression to AML used criteria by the International Working Group (IWG) Response Criteria in Myelodysplasia (Cheson, 2006). Progression is considered if any of the following are met: - \>=50% increase in blasts - \>=50% decrement from maximum remission/response levels in granulocytes or platelets - Reduction in Hgb concentration by \>=2 g/dL - Transfusion dependence This outcome was defined as a Kaplan-Meier estimate however few participants progressed so a Kaplan-Meier analysis could not be performed. Disclosed are time to progression values only for participants who did progress to AML.

Time frame: Day 1 to 183.7 weeks

Time to Progression to Events of Higher Risk Myelodysplastic Syndromes (MDS) Using the International Prognostic Scoring System (IPSS) For Participants Who Had Progression

Progression to events of higher risk MDS used criteria from the International Prognostic Scoring System for MDS (IPSS) which assigns a prognostic score (0=good and increasing in risk by half-grades with the top score outlined below) for three prognostic variables: - Marrow blasts (score 0-2.0) - Karyotype (score 0-1.0) - Cytopenias: neutrophil, platelets, and Hg counts (score 0-0.5) The three individual scores are summed resulting in a full range of 0- 3.5 and placed into risk categories 0 = low risk 0.5-1.0 = intermediate-1 risk 1.5-2.0 = intermediate-2 risk \>=2.5 = high risk This outcome was defined as a Kaplan-Meier estimate however few participants progressed so a Kaplan-Meier analysis could not be performed. Data reported represent event times (weeks) for participants who did progress to higher risk MDS categories.

Time frame: Day 1 to 257.3 weeks

Kaplan-Meier Estimates for Progression-free Survival

Participants who had disease progression were considered to have events. Participants who died without acute myeloid leukemia (AML) were also considered to have events with the event date as the date of death. Those who did not have disease progression and who were lost to follow-up were censored at the last known disease progression assessment date. Participants without disease progression at the last follow-up contact were censored at the date of the last follow-up contact date. Disease Progression to AML used criteria by the International Working Group (IWG) Response Criteria in Myelodysplasia (Cheson, 2006). Progression is considered if any of the following are met: - \>=50% increase in blasts - \>=50% decrement from maximum remission/response levels in granulocytes or platelets - Reduction in hemoglobin (Hgb) concentration by \>=2 g/dL - Transfusion dependence

Time frame: Day 1 to 257.3 weeks

Kaplan-Meier Estimates for Overall Survival (OS)

OS was defined as the time between start of treatment and the death/censored date. Participants who died (regardless of the cause of death) were considered to have an event. Participants who were alive at the end of the study, and participants who were lost to follow-up, were censored at the last date when subjects were known to be alive.

Time frame: Day 1 to 257.3 weeks

Pharmacokinetic Parameters of Sotatercept: Serum Concentration at Various Study Timepoints

Maximum observed serum concentration, obtained directly from the observed concentration versus time data.

Time frame: Cycle 1 Day 8 and !5 up to Cycle 2 Day 1

Participants With Treatment-Emergent Adverse Events (TEAE)

An adverse event (AE) is any noxious, unintended, or untoward medical occurrence that may appear or worsen in a subject during the course of a study. Treatment-emergent adverse events (TEAEs) are defined as any AE occurring or worsening on or after the first treatment of the study medication and within 42 days after the last dose. The severity of AEs was graded based on National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE), Version 4.0 and the scale: Grade 1 = Mild Grade 2 = Moderate Grade 3 = Severe Grade 4 = Life threatening Grade 5 = Death. Relation to study drug was determined by the investigator. A treatment-related TEAE is defined as TEAE which was considered to be related to the study drug and reported as 'Suspected' on the CRF. AEs with a missing relationship were treated as 'treatment-related' in data summaries.

Time frame: Day 1 up to 59.2 months

Dose Limiting Toxicities (DLTs)

The following were DLTs if the investigator suspected they were treatment related: 1. Increase to \>= 140 mmHg systolic blood pressure 2. Increase to \>=90 mmHg diastolic blood pressure 3. Increase to \>=140 systolic and increase \> 20 mmHg compared to baseline systolic 4. Increase to \>=90 mmHg diastolic and increase \> 20 mmHg compared to baseline diastolic 5. Introduction of new anti-hypertension medication during treatment 6. Increase in dose of baseline anti-hypertension medication during treatment 7. \>= Grade 2 (moderate severity or worse) hypertension as an adverse event

Time frame: Day 1 to 59.2 months

Number of Participants Who Achieved Red Blood Cell (RBC)-Transfusion Independence During the Erythroid Hematological Improvement (HI-E) Interval

Number of participants who achieved RBC-independence was defined as participants who required no RBC-transfusions during a 56-day interval of erythroid hematological improvement (HI-E). NTDE = non-transfusion dependence efficacy participants who required \< 4 units of RBCs in the 8 weeks prior to start of therapy TDE = transfusion dependence efficacy participants who required \>=4 units of RBCs in the 8 weeks prior to start of therapy

Time frame: Day 2 to Day 142