• Clinical science

Myeloproliferative neoplasms


Myeloproliferative neoplasms (MPN) are a group of disorders characterized by a proliferation of malignant hematopoietic stem cells that belong to the myeloid cell lineage. The most clinically relevant MPN include chronic myeloid leukemia (CML), polycythemia vera (PV), primary myelofibrosis (PMF), and essential thrombocythemia (ET). An important etiological factor is the mutation of the Janus kinase-2 (JAK2) gene, which is present in almost all cases of PV and in approximately 50% of patients with ET and PMF. In contrast to the other subtypes, CML is characterized by a distinct translocation between chromosome 9 and 22 (BCR-ABL1 fusion gene). Each of these neoplasms has a typical pattern of cell proliferation: granulocytes are increased in CML, thrombocytes in ET, and all cell lines show increased proliferation in PV. PMF, on the other hand, shows an initial hyperproliferative phase, but eventually progresses to pancytopenia. All myeloproliferative neoplasms may lead to elevated uric acid levels and gout as a result of increased cellular breakdown. They are also associated with an increased risk of acute myeloid leukemia. Treatment involves hydroxyurea to reduce the cell count, polychemotherapy to halt the proliferation of malignant cells, and, in young patients, allogeneic stem cell transplantation.


According to the WHO classification, the following disorders belong to the group of myeloproliferative neoplasms:

With the exception of CML, all of these disorders show varying degrees of JAK2 mutations, which can be used as a diagnostic marker. The mutation causes the exchange of two amino acids (valinephenylalanine), which, in turn, results in dysregulation of the tyrosine kinase JAK2.


Primary myelofibrosis

Clinical features



In myelofibrosis, RBCs shed tears (teardrop cells), because they have been forced out of the fibrosed bone marrow (extramedullary hematopoiesis).


Essential thrombocythemia

Clinical features


ET is a diagnosis of exclusion; all other causes of thrombocytosis must be ruled out before the diagnosis can be made.

Differential diagnosis



Chronic eosinophilic leukemia