Ruxolitinib, a selective JAK1/JAK2 inhibitor, is the current first line therapy for myelofibrosis (MF), which reduces symptomatology and splenomegaly, but does not clearly modify disease course.
"Driver" mutations in JAK2, MPL and indels in CALR underlie the vast majority of cases of PMF and post-ET MF; the remainder (≈ 10%) lack identifiable driver mutations, but other clonal markers are usually detectable.
Approximately 6% and 14% of JAK2V617F-negative essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients, respectively, have 'canonical' MPL exon 10 driver mutations W515L/K/R/A or S505N, which generate constitutively active receptors and consequent loss of Tpo dependence.
Conversely, mice carrying the hypomorphic Gata1<sup>low</sup> mutation express an activated TPO/JAK2 pathway and partially respond to JAK inhibitors in a fashion similar to PMF patients (reduction of spleen size but limited improvement of the natural history of the disease).
Approximately 6% and 14% of JAK2 V617F-negative essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients, respectively, have 'canonical' MPL exon 10 driver mutations W515L/K/R/A or S505N, which generate constitutively active receptors and consequent loss of Tpo dependence.
Moreover, 4 therapeutic JAK2 inhibitors (ruxolitinib, fedratinib, momelotinib, and pacritinib) have either been approved or are in advanced clinical development for myelofibrosis.
Primary Myelofibrosis (PMF) is a myeloproliferative disorder associated with JAK2V617F, Calreticulin (CALR) indels, and MPLW515L/K mutations activating the tyrosine kinase JAK2 and its downstream signaling pathway.
In the current study, we have increased the number of informative cases from 130 to 414 (median age 63 years; 63% males), in order to revisit with the phenotypic and prognostic relevance of the JAK2 46/1 haplotype in PMF.
The advances in molecular insights, especially the discovery of the Janus kinase 2 (JAK2) V617F mutation and its role in JAK-STAT pathway dysregulation, led to the development of the JAK inhibitor ruxolitinib, which currently represents the cornerstone of medical therapy in MF and hydroxyurea-resistant/intolerant PV.
The discovery of mutations in JAK2, CALR, and MPL have uncovered activated JAK-STAT signaling as a primary driver of MF, supporting a rationale for JAK inhibition.
We conclude that besides morphology of megakaryocytes and other features, JAK2V617F allelic burden can help differentiate CMML from PMF with monocytosis.
An integral part of laboratory tests carried out in this disease group is detecting the presence of mutations in the Janus kinase 2 gene at position 617 (JAK2 V617F) and in the gene encoding for the receptor for thrombopoietin (myeloproliferative leukemia virus oncogene, MPL) found in approximately 60% of PMF patients.
A JAK2 variant in addition to JAK2V617F (n = 13) in myelofibrosis was associated with an increased cumulative risk of transformation into AML (P = .003).
Whether noncanonical and/or concomitant JAK2- and MPL-mutations exist in myelofibrosis (MF) regardless of phenotype-driver mutations is not yet elucidated.
Immune thrombocytopenia is associated with persistently deranged fibrosis-related seromarker profiles but low bone marrow fibrosis grades: A 2-year observational study on thrombopoietin receptor agonist treatment.
ABSTRACT: Background The BCR-ABL-negative myeloproliferative neoplasms, i.e., polycythemia vera, essential thrombocythemia (ET), and myelofibrosis (MF), are characterized by mutations in JAK2, CALR, or MPL.
ABSTRACT: Background The BCR-ABL-negative myeloproliferative neoplasms, i.e., polycythemia vera, essential thrombocythemia (ET), and myelofibrosis (MF), are characterized by mutations in JAK2, CALR, or MPL.
In fact, exome sequencing revealed that most patients with essential thrombocythemia (ET) or primary myelofibrosis (PMF) lacking JAK2 or MPL mutations, harbor somatic insertion and/or deletion in exon 9 of CALR gene.