The JAK2^V617F tyrosine kinase mutation in myelofibrosis with myeloid metaplasia: Lineage specificity and clinical correlates

An association between an activating JAK2 mutation (JAK2^V617F) and BCR/ABL-negative myeloproliferative disorders was recently reported in multiple simultaneous publications. In the current study, mutation analysis for JAK2^V617F was performed in peripheral blood mononuclear cells (PBMC) from 157 patients with myelofibrosis with myeloid metaplasia (MMM) including 117 with agnogenic (AMM), 22 with postpolycythaemic (PPMM), and 18 with post-thrombocythaemic (PTMM) myeloid metaplasia. The detection rate for JAK2^V617F was significantly higher in PPMM (91%; homozygous in 18%) compared with either AMM (45.3%; homozygous in 2.6%) or PTMM (38.9%; homozygous in 11.1%). Concomitant analysis in granulocytes (n = 57) and CD34⁺ cells (n = 25) disclosed a higher incidence of homozygous JAK2^V617F mutation but the overall mutation rate was similar to that obtained from PBMC. JAK2^V617F was not detected in DNA derived from T cells (n = 19). In AMM, the presence of JAK2^V617F was associated with an older age at diagnosis and a history of thrombosis or pruritus. Multivariate analysis identified only age and the Dupriez prognostic score as independent prognostic factors; JAK2^V617F had no prognostic significance. In conclusion, JAK2^V617F is a myeloid lineage-specific event, its incidence in MMM is significantly higher with an antecedent history of polycythaemia vera (PV), and its presence in AMM does not affect prognosis but is associated with PV-characteristic clinical features.