Novel <b><i>JAK2</i></b> Exon 14 Mutations L611S or N622Y in cis with <b><i>JAK2</i></b><sup>V617F</sup> Are Associated with Distinct Clinical Phenotype of Polycythemia Vera and Concurrent Eosinophilia

Eosinophilic phenotypes in polycythemia vera (PV) and essential thrombocythemia (ET) are rare and poorly characterized. Co-occurring JAK2 mutations in cis, specifically L611S or N622Y mutations, appear to result in a more aggressive clinical phenotype. PV/ET with eosinophilic phenotypes may require full next-generation sequencing to capture co-occurring mutations as opposed to more prevalent single-gene assays. These eosinophilic phenotypes are highly thrombotic and systemic symptoms appear responsive to early use of the janus kinase inhibitor ruxolitinib.