The impact of clinicopathological studies on staging and survival in essential thrombocythemia, chronic idiopathic myelofibrosis, and polycythemia rubra vera

In chronic myeloproliferative disorders (MPDs), varying results regarding staging of disease and assessment of outcome have been reported. Risk classification is mainly based on clinical data; however, in those disorders associated with an elevated platelet count, discrimination of (true) essential thrombocythemia (ET) may be difficult without the possibility to recognize characteristic histopathological bone marrow patterns according to the World Health Organization (WHO) guidelines. Patients with ET reveal no relevant reduction of life expectancy and the impact of disease is significantly higher in elderly patients, especially in chronic idiopathic myelofibrosis (IMF) and polycythemia rubra vera (PV). In high-risk ET, the overall incidence of myelofibrotic transformation after 36 months of follow-up is 2.8% when considering the Polycythemia Vera Study Group guidelines. In contrast, classification according to WHO fails to show a relevant transformation into myelofibrosis either by clinical or morphological standards in (true) ET. Early stages of IMF show a more favorable outcome, but in multivariate risk classification, signs of myeloid metaplasia have the most important impact on prognosis. In PV, the risk for thrombosis increases with age, and furthermore, signs of generalization are generally associated with a worsening of prognosis. It has been shown that examination of bone marrow specimens enhances the diagnostic reliability and also enables the recognition of evolving myelofibrotic transformation in MPDs.