This is a multicentric, observational, retro-prospective study in adult PV patients - resistant or intolerant to hydroxyurea - who are going to receive or have already initiated treatment with ruxolitinib according to the approved local label. Enrolment will last 9 months after the first enrolled patient. Patients will be observed for a minimum of 3 months, in order to evaluate the primary endpoint for all patients.

This is a multicentric, observational, retro-prospective study in adult population who have been diagnosed with polycythemia vera according to the 2022 (WHO or ICC) criteria, who are resistant or intolerant to hydroxyurea and who are going to be prescribed or have already initiated treatment with ruxolitinib according to the approved local label. Patients who started treatment with ruxolitinib - according to clinical practice - will be enrolled. Enrolment will last 9 months after the first enrolled patient. Patients will be observed for a minimum of 3 months, in order to evaluate the primary endpoint for all patients.

Inclusion Criteria:

1. Patients aged ≥ 18 years of age
2. Subjects must be diagnosed with PV according to the 2022 World Health Organization (WHO) or International Consensus Classification (ICC) criteria
3. Subjects must have a treatment history for PV that meets the definition of resistance or intolerance to hydroxyurea (HU) in accordance with the indications of the Italian Medicines Agency
4. Patients already on ruxolitinib treatment (retrospective cohort) at the start date of the study or patients who will start ruxolitinib (prospective cohort) during the study enrollment
5. Signed informed consent

Exclusion Criteria:

1. Different diagnosis from PV [eg. other chronic myeloproliferative neoplasia such as essential thrombocythemia, myelofibrosis; or of congenital erythrocytosis or secondary erythrocytosis]

Patients with a diagnosis of Polycythemia vera according to WHO or ICC 2022 criteria who received treatment with ruxolitinib as second-line therapy for resistance / intolerance to hydroxyurea, according to the prescription criteria approved in Italy. Patients already on treatment (retrospective part) at the start date of the study and patients included after the start date for a period of 9 months may be included in the study