Diagnostic Usefulness of the Janus Kinase 2 Mutation in non BCR/ABL Myeloproliferative Disorders

BACKGROUND: We investigated the Janus kinase 2 (JAK2) mutation and its diagnostic value in patients suffering with non BCR/ABL myeloproliferative diseases (nMPD) or other reactive conditions. METHODS: We reviewed the clinical records of 83 patients who underwent bone marrow (BM) examinations with suspect of nMPD. The diagnoses of nMPD were made based on the WHO criteria since 2001 and the PVSG criteria before 2001. The JAK2 mutation was examined by PCR in 54 patients whose BM samples were available. RESULTS: The JAK2 mutation was detected in 25 patients (46%); 12 of 26 patients with essential thrombocythemia (ET), 9 of 12 patients with polycyhtemia vera (PV), one of 7 patients with chronic idiopathic myelofibrosis (CIM) and one patient with unclassifiable MPD. Additionally, JAK2 mutation was detected in each one patient with secondary polycythemia and reactive thrombocytosis. These two patients and two other patients among the JAK2 mutated ET did not meet the WHO PV criteria due to their initial low hemoglobin levels. These patients had liver cirrhosis and hypersplenism due to Budd-Chiari syndrome (1), gastrointestinal bleeding (1) or the initial hemoglobin level was slightly below the level as provided by the criteria, but the level showed a rising pattern despite cytoreductive therapy (2). With the results of the JAK2 mutation available, 4 patients' disease could be re-diagnosed as PV. Finally, the positive rate of the JAK2 mutation was 81% in PV, 48% in ET and 14% in CIM. The presence of JAK2 mutation closely correlated with PV (p=0.001), leukocytosis (p=0.001) and an increased cellularity of BM (p=0.024). CONCLUSIONS: The JAK2 mutation may help differentiate nMPD from secondary cytosis. Therefore, it should be incorporated into the guidelines for the nMPD work-up for making a more accurate diagnosis and administering proper treatment.