| Inclusion Criteria: | 1) MPN-associated myelofibrosis
2) Anemic patient OR RBC-transfusion-dependent patient
3) Equal to or greater than 18 years of age
4) ALT (SGPT) and AST (SGOT) equal to or less than 2.5x upper limit of normal (ULN), or equal to or less than 4x ULN (if upon judgment of the treating physician, it is believed to be due to extramedullary hematopoiesis [EMH] related to MF)
5) Direct bilirubin equal to or less than 1.5 x ULN; or equal to or less than 2x ULN (if upon judgment of the treating physician, it is believed to be due to extramedullary hematopoiesis related to MF)
6) Serum creatinine equal to or less than 2.5 mg/dL
7) Treatment-related toxicities from prior therapies must have resolved to Grade equal to or less than 1
8) Women of childbearing potential and men must agree to using medically approved (i.e., mechanical or pharmacological) contraceptive measure for at least 112 days following the last dose of sotatercept (ACE-011), Males must agree to use a latex condom or non-latex condom NOT made of natural (animal) membrane during any sexual contact with females of childbearing potential or a pregnant female while participating in the study and for at least 112 days following the last dose of sotatercept (ACE-011), even if he has a vasectomy. |