IRAK1 and Thrombocytopenia: Pacritinib appears to elicit significant spleen responses in patients with the “myelodepletive phenotype” of MF or cytopenic MF, which has been associated with anemia, thrombocytopenia, JAK2 V617F variant allele frequencies below 50%, and smaller spleen size [53, 54]; efficacy in this subgroup, associated with a poor prognosis, may be attributed to the inhibitory activity of pacritinib on IRAK1 [37].