A prognostic model to predict survival in 867 WHO-defined essential thrombocythemia at diagnosis: a study by the IWG-MRT.

Diagnosis of essential thrombocythemia (ET) has been updated in the last World Health Organization (WHO) classification. We developed a prognostic model to predict survival at diagnosis, named IPSET (International Prognostic Score for ET), studying patients with WHO-defined ET. Age equal to or over 60 years, leukocyte count equal to or greater than 11 x10(9)/L and prior thrombosis significantly affected survival, by multivariable Cox regression. On the basis of the hazard ratio, we assigned two points to age and one each to leukocyte count and thrombosis. So, the IPSET model allocated 867 patients into three risk categories with significantly different survival: low (sum of points=0; median survival not reached), intermediate (sum=1-2; median survival 24.5 years), and high (sum=3-4, median survival 13.8 years). The IPSET model was further validated in two independent cohorts including 132 WHO-defined ET and 234 PVSG-defined ET patients. The IPSET model was able to predict the occurrence of thrombosis, and not to predict post-ET myelofibrosis. In conclusion, IPSET, based on age ≥ 60 years, leukocyte count ≥ 11 x10(9)/L and history of thrombosis allows prognostic assessment of WHO-defined ET and the validation process makes IPSET applicable in all patients phenotypically appearing as ET.