RecruitingRuxolitinib in Primary Myelofibrosis and Secondary to Essential Thrombocythemia or Polycythemia VeraThe 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.