The study is observational multicenter retrospective and prospective cohort study of patients with primary or secondary myelofibrosis who have initiated therapy with ruxolitinib, prescribed as part of the normal course of care and completely independent of study participation. The primary purpose is to determine the impact of clinical and laboratory characteristics of myelofibrosis on the prognosis of patients treated with ruxolitinib, understood as long-term survival.

The study is observational multicenter retrospective and prospective cohort study of patients with primary or secondary myelofibrosis who have initiated therapy with ruxolitinib, prescribed as part of the normal course of care and completely independent of study participation. Laboratory tests and histological, cytogenetic, molecular, and radiological investigations performed by the patient and collected for study will be conducted in accordance with clinical practice, independent of the patient's participation in the study. In particular. data on systemic symptoms and splenomegaly will be collected at diagnosis and disease reassessments performed in the context of normal clinical practice. The minimum planned duration of individual patient observation is 3 months and the planned duration of the study is 10 years.

Inclusion Criteria:

• Age ≥ 18 years
• Patients diagnosed with Primary Myelofibrosis or secondary to Essential Thrombocythemia/Polycythemia vera who are being treated or have been treated with ruxolitinib therapy in accordance with normal clinical practice.
• Availability of data on clinical history prior to initiation of Ruxolitinib therapy
• Obtaining informed consent for data collection and processing

Exclusion Criteria:

• None

The study is observational multicenter retrospective and prospective cohort will be offered consecutively to any patient with primary or secondary myelofibrosis who has initiated therapy with ruxolitinib, prescribed as part of the normal course of care and completely independent of study participation. The study will be conducted in the study-participating OUs of Hematology, and an estimated total of 1015 patients who initiated therapy with Ruxolitinib between 2008 and the end of the study are expected to participate in this study.