Ruxolitinib (INCB018424, Incyte, Wilmington, DE) is a small molecule JAK1/2 tyrosine kinase inhibitor that is approved by the US Food and Drug Administration (FDA) to treat certain MPNs, including myelofibrosis (MF) and polycythemia vera (PV)6–8. The gene discussed is JAK1; the disease is myelofibrosis.