The main aim of this study is to find out how well elritercept works to improve anemia in participants with myelofibrosis (MF) who are taking ruxolitinib when compared to placebo.
Other aims are to learn how elritercept improves anemia compared to placebo; to learn if elritercept reduces tiredness, improves symptoms related to MF, and helps participants do physical activities more easily. The study also aims to find out how elritercept affects the bone marrow, the spleen, and whether participants develop antibodies to the study drug.
The study will also check how safe elritercept is compared to placebo, and if elritercept stays safe over a long period of time. Participants will receive study treatment for at least 9 months (36 weeks). After this period, participants who received placebo will have the option to switch to elritercept.