INTRODUCTION: Myelofibrosis (MF) is a clonal haematological disease associated 
with recurrent somatic gene mutations (JAK2V617F, MPL, CALR) and constitutive 
activation of the Janus kinase (JAK)/Signal Transducer and Activator of 
Transcription pathway. MF is often characterised by debilitating symptoms and 
JAK inhibitors (JAKIs) have revolutionised available therapeutic options. 
Ruxolitinib, a JAK1 and 2 inhibitor, is the only currently approved agent. 
Several other JAKIs are undergoing evaluation in the clinical trial setting and 
Pacritinib , a novel JAK2 and FLT3 inhibitor, is at an advanced stage of 
investigation with recent completion of a Phase III trial and another ongoing.
AREAS COVERED: Within this article we focus on pacritinib, summarising the 
development, preclinical and up-to-date results from the Phase I - III trials. 
We present the most recent data on efficacy and safety and indirectly compare 
this novel JAKI with ruxolitinib.
EXPERT OPINION: The kinome array data for pacritinib suggests that it has a 
range of targets differing to those for ruxolitinib. Pacritinib appears to be an 
effective agent for the control of MF-related symptoms and splenomegaly with 
potentially fewer haematological side-effects when compared with ruxolitinib and 
seems a particularly promising agent for anaemic and thrombocytopenic patients. 
It is also an attractive drug for potential combination studies due to its good 
tolerability.