The purpose of this study is to determine real-world patient-reported outcomes with fedratinib (FEDR) therapy for myelofibrosis (MF) in the real-world (RW) setting.

Inclusion Criteria:

• Diagnosed with Primary myelofibrosis (PMF), post- Essential thrombocythemia (ET) Myelofibrosis (MF), or post- Polycythemia vera (PV) MF
• Treated with FEDR and initiated treatment after 16 August 2019.
• Received prior treatment with RUX.
• Had spleen assessed at time of initiation of FEDR by palpation.
• Able to read and speak English
• Willing to provide informed consent
• Willing to provide permission to the site to release her/his medical information to the study investigators according to the study-specific eCRF
• Willing to complete the baseline survey prior to first FEDR

Exclusion Criteria:

• Past or current participant in any FEDR-related clinical trial

The study population will consist of participants who have discontinued RUX and will be initiating FEDR prospectively.