ACVR1 and Splenomegaly: Pacritinib is a JAK1-sparing inhibitor of JAK2/FLT3/IRAK1/activin A receptor type 1 (ACVR1) that has received accelerated FDA approval for patients with splenomegaly and/or symptoms and severe thrombocytopenia (platelet counts <50 × 109/L) [12].