The classic, Bcr/Abl-negative myeloproliferative neoplasms (MPN, MPD) include polycythemia vera (PV), primary myelofibrosis (PMF, AMM, MMM, chronic idiopathic myelofibrosis), and essential thrombocythemia (ET, primary or essential thrombocytosis) . Other members of MPN include chronic myeloid leukemia (CML), chronic neutrophilic leukemia, systemic mastocytosis, chronic eosinophilic leukemia-not otherwise specified and MPN-unclassifiable.
The MPD are themselves a subcategory of chronic myeloid disorders that also include chronic myeloid leukemia (CML), myelodysplastic syndrome (MDS), MDS/MPN and myeloid/lymphoid malignancies associated with eosinophilia and rearrangements of PDGFRA, PDGFRB or FGFR1. (See "Overview of the myeloproliferative neoplasms".)
ET is neither a cytogenetically nor a morphologically defined disease entity, but rather is a diagnosis of exclusion. Thus, the diagnosis of ET requires that both reactive thrombocytosis and other chronic myeloid disorders have been excluded . This review will discuss the prognosis and treatment of ET [3-6]. The general approach to the patient with an elevated platelet count and the diagnosis and clinical manifestations of ET are discussed separately. (See "Approach to the patient with thrombocytosis" and "Diagnosis and clinical manifestations of essential thrombocythemia".)
Most patients with ET enjoy a normal life expectancy without associated disease-related complications [7,8]. In morphologically and cytogenetically defined ET (ie, patients in whom PV, CML, MDS, and PMF have been excluded), the delayed development of either acute myeloid leukemia (AML) or post-ET myelofibrosis (post-ET MF) is unusual [9,10]. As examples:
- In a large retrospective study of 435 patients with ET, the 15-year cumulative risks of thrombosis and clonal evolution into either AML or post-ET MF were 17, 2, and 4 percent, respectively .
- In an international study of 891 patients with ET confirmed by the use of WHO criteria, 15-year cumulative risks of thrombosis, leukemic transformation, or overt fibrotic progression were 22, 2, and 9 percent, respectively . Overall survival (median survival: 14.7 years) was similar to that of the sex- and age-standardized European population.