Study to Evaluate the Long-term Safety of Rusfertide (PTG-300) in Subjects With Polycythemia Vera

Inclusion Criteria: * Subject who has completed at least 12 months of dosing with rusfertide and successfully completed the end of treatment visit of a previous Phase 2 study of rusfertide. * Subject understands the study procedures, is willing and able to adhere to study requirements and agrees to participate in the study by giving written informed consent. Key Exclusion Criteria: * Subject who, in the opinion of the investigator, should not participate in the study. * Subject who discontinue early from a previous rusfertide study for reasons other than enrolling in this study. * Pregnant or lactating females. * Women of childbearing potential (WOCBP) who do not agree to use medically acceptable contraception (\<1% annual failure rate) during the study and for 30 days after the last dose of study drug. * Men with partners of childbearing potential who do not agree to use medically acceptable contraception (\<1% annual failure rate) during the study and for 90 days after the last dose of study drug. * Men who do not agree to use a condom during the study and for 90 days after the last dose of study drug regardless of the partner's childbearing potential. * A female subject intends to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study and for a period of 30 days after receiving the last dose of study drug. * A male subject intends to donate sperm for the purpose of reproduction during the study and for a minimum of 90 days after receiving the last dose of study drug. * Plan to use investigational treatment other than rusfertide during the course of the study or within 28 days after last rusfertide dose. * Subject with hypersensitivity to rusfertide or to any of the excipients. * In the investigator's opinion the subject has progressive disease that cannot be managed by adjusting concurrent cytoreductive therapy.