Myelofibrosis (MF) is a rare blood cancer, characterized by extensive fibrosis (scarring) of the bone marrow. It is one of a group of cancers known as myeloproliferative neoplasms (MPNs) in which bone marrow cells that produce blood cells develop and function abnormally. This study will evaluate treatment patterns, treatment outcomes, healthcare resource utilization in adult participants with Myelofibrosis.

Data from approximately 1000 participants will be collected. No participants will be enrolled in this study.

Participants' charts will be reviewed. No drug will be administered as a part of this study. The duration of the observation period is up to 156 weeks.

There is no additional burden for participants in this trial. All visits must be completed prior to data extraction and participants will be followed for up to 156 weeks.

Inclusion Criteria:

• Treated for myelofibrosis (MF) [primary myelofibrosis (PMF) and secondary myelofibrosis (SMF)].
• Must have initiated their first treatment on or after the first date when ruxolitinib was approved in their country of residence and no later than 31 December 2021.

Exclusion Criteria:

- Having received MF treatment in a clinical trial setting.

Adult participants patients diagnosed with myelofibrosis and treated on or after the first date when ruxolitinib was approved in their country of residence and no later than 31 December 2021.