Unexpectedly, selective nanomolar IRAK1 inhibition was detected in a kinome-wide screening study for the JAK2/FLT3 inhibitor, pacritinib, which is in late stage development for patients with myelofibrosis (MF) and other myeloproliferative neoplasms (MPNs) [29–31]. Here, IRAK1 is linked to myelofibrosis.