INCB039110 is an effective JAK1 inhibitor with >20-fold selectivity over JAK2 and >100-fold over JAK3 and TYK2.323 In an open-label phase II trial (NCT01633372), myelofibrosis-related symptoms were obviously ameliorated after INCB039110 treatment. This evidence concerns the gene JAK2 and myelofibrosis.