JAK1 and myelofibrosis: As a result, the development of inhibitors of tyrosine kinases of the JAK family has emerged as a promising therapeutic approach in recent years, including myelofibrosis.[155] The small molecule pacritinib is selective for the isoform JAK2 as it does not inhibit JAK1 or JAK3.[156] It is dysfunction in the JAK2 signaling pathway that is associated with myelofibrosis.