Criteria according to the and the . A diagnosis of ET is established when all major diagnostic criteria are met or when the first three major criteria and one minor criterion are fulfilled.

Where neither a driver mutation nor another clonal marker is found, reactive causes such as iron deficiency, chronic infection or inflammation, or a previous splenectomy are to be excluded.

Major diagnostic criteria

• Platelet count of 450 x 109/L or above
• Bone marrow biopsy with proliferation mainly of the megakaryocytic lineage, increased numbers of enlarged, mature megakaryocytes with hyperlobulated, staghorn-like nuclei and infrequent dense clusters, no significant increase or left shift of neutrophil granulopoiesis or erythropoiesis and no relevant fibrosis
• Criteria for BCR::ABL1-positive chronic myeloid leukaemia (CML), PV, PMF, or another myeloid neoplasm are not met
• JAK2, CALR or MPL mutation

Minor diagnostic criteria

• Presence of a clonal marker, or absence of evidence of reactive thrombocytosis

Criteria according to the and the . A diagnosis of post-ET myelofibrosis is established when both essential criteria are met or when at least two additional criteria are fulfilled.

Essential diagnostic criteria

• History of (WHO-defined) ET
• Bone marrow fibrosis of grade 2-3

Additional diagnostic criteria

• Anaemia and a > 2 g/dL decrease from baseline haemoglobin concentration
• Leukoerythroblastosis
• Splenomegaly (increase in palpable splenomegaly of > 50 mm from baseline or newly palpable splenomegaly)
• Development of ≥2 symptoms: > 10% weight loss in 6 months, night sweats, or unexplained fever (> 37.5°C)
• Elevated LDH level

JAK2 V617F is found in about 60% of patients, CALR mutations in about 20% and MPL mutations in about 3%; a small group carries none of the three. In an NGS series, about half of the patients carried additional non-driver mutations, most frequently in TET2 and ASXL1. The main differential diagnosis is prefibrotic PMF (pre-PMF), marked by large dense clusters of more than six megakaryocytes with granulocytic proliferation. In comparison, patients with ET usually have normal leukocyte counts, no anaemia, a normal lactate dehydrogenase and less frequent splenomegaly.

Chromosome analysis

Chromosome analysis detects numerical and structural chromosomal aberrations and complex karyotypes and provides diagnostic and prognostic information. In ET, it serves to exclude other myeloid neoplasms with thrombocytosis, such as myelodysplastic neoplasms with del(5q) or inv(3)/t(3;3).

FISH

FISH detects defined rearrangements, deletions and numerical changes on interphase nuclei. No FISH finding defines ET. BCR::ABL1 is to be excluded, since the criteria of chronic myeloid leukaemia must not be met.

Molecular genetics

Molecular analyses serve to detect disease-relevant genetic alterations and contribute substantially to diagnosis, prognostic assessment, and treatment planning. Where ET is suspected, JAK2 V617F, CALR and MPL are determined; in negative cases, a search for noncanonical JAK2 and MPL mutations should be considered. An SF3B1 mutation, usually together with JAK2 V617F, points to myelodysplastic/myeloproliferative neoplasm with thrombocytosis and an SF3B1 mutation. The analyses offered are listed in the table below.

Orderable analyses

Table 1: analyses offered by Medicover. BM – bone marrow, TAT – turnaround time.

Essential thrombocythaemia (ET) is generally an indolent disease with a favourable prognosis. Many patients remain symptom-free for years and have a near-normal life expectancy. Nevertheless, ET is associated with an increased risk of blood clots and bleeding, and approximately 10–15% of patients may progress to myelofibrosis over time. The current revised IPSET-thrombosis combines age, previous thrombosis and JAK2 mutation status into four categories: very low risk at 60 years or below without thrombosis and without a JAK2 mutation, low risk with the same features but a JAK2 mutation, intermediate risk above 60 years without thrombosis and without a JAK2 mutation, and high risk with previous thrombosis, or above 60 years with a JAK2 mutation. Mutations in SH2B3, SF3B1, U2AF1, TP53, IDH2 and EZH2 are associated with a less favourable course, TP53 with leukaemic transformation, and MPL and CALR type 1 mutations with progression to myelofibrosis. Treatment is tailored to an individual’s risk profile and aims to prevent disease-related complications.

For post-ET myelofibrosis, the MYSEC-PM is the validated score; it combines haemoglobin below 11 g/dL, circulating blasts of 3% or more, unmutated CALR, a platelet count below 150 x 109/L, constitutional symptoms and age. A calculator is available at .

Treatment indications, options and algorithms for ET are set out by the Onkopedia guidelines and by the National Comprehensive Cancer Network. This page does not reproduce them.

• Onkopedia, Essential (or primary) thrombocythemia (ET), short version, August 2021:
• Onkopedia myelofibrosis guideline 2025, including post-ET myelofibrosis:
• NCCN Clinical Practice Guidelines in Oncology, Myeloproliferative Neoplasms:

This page does not give treatment recommendations. Therapy decisions should follow the guidelines referenced above and the protocols of the responsible study group.

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