Inclusion Criteria:  adults (age ≥18 years), affiliated to the national social security system, with CALR mutated myeloproliferative neoplasm diagnosed between 2006 - 2020, for which at least one sample is available at the time of diagnosis or before cytoreductive treatment, who signed the consent to participate in the study, included, or consenting to be included, in the national clinical-biological database of France Intergroupe Syndrome Myéloprolifératifs (FIM).  Exclusion Criteria:  patient with another active hematological disease or cancer at the time of diagnosis, person subject to legal protection scheme or incapable of giving consent.