Purpose: Myeloproliferative neoplasms (MPNs) are characterized by the overproduction of differentiated myeloid cells. Mutations in JAK2, CALR and MPL are considered drivers of Bcr-Abl-ve MPNs, including essential thrombocythemia (ET), polycythemia vera (PV), prefibrotic primary myelofibrosis (prePMF) and overt myelofibrosis (MF). However, how these driver mutations lead to phenotypically distinct and/or overlapping diseases is unclear. Experimental Design: To compare the genetic landscape of MF to ET/PV/PrePMF, we sequenced 1711 genes for mutations along with whole transcriptome RNA-seq of 137 MPN patients. Results: In addition to driver mutations, 234 and 74 genes were found to be mutated in overt MF (N=106) and ET/PV/PrePMF (N=31), respectively. Overt MF had more mutations compared to ET/PV/prePMF (5 vs 4 per subject, P=0.006). Genes frequently mutated in MF included high-risk genes (ASXL1, SRSF2, EZH2, IDH1/2 and U2AF1), and Ras pathway genes. Mutations in NRAS, KRAS, SRSF2, EZH2, IDH2 and NF1, were exclusive to MF. Advancing age, higher DIPSS and poor overall survival (OS) correlated with increased variants in MF. Ras mutations were associated with higher leukocytes and platelets, and poor OS. The comparison of gene expression showed upregulation of proliferation and inflammatory pathways in MF. Notably, ADGRL4, DNASE1L3, PLEKHGB4, HSPG2, MAMDC2 and DPYSL3 were differentially expressed in hematopoietic stem and differentiated cells. Conclusions: Our results illustrate that evolution of MF from ET/PV/PrePMF likely advances with age, accumulation of mutations, and activation of proliferative pathways. The genes and pathways identified by integrated genomics approach provide insight into disease transformation and progression, and potential targets for therapeutic intervention.
