JAK2 and acquired polycythemia vera: These findings nicely dovetailed with the data reported at the same time by Levine et al. [32], who detected in the great majority of myeloproliferative syndromes-and in particular in almost all cases of polycythemia vera-a V617F mutation occurring in the coding sequence of the Janus kinase 2 (JAK2) that constitutively activated this receptor-associated tyrosine kinase, resulting in turn in the strong activation of STAT5.