"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.
Whether noncanonical and/or concomitant JAK2- and MPL-mutations exist in myelofibrosis (MF) regardless of phenotype-driver mutations is not yet elucidated.
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.
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.
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.
Key differences from the 2011 diagnostic recommendations included: lower threshold values for hemoglobin and hematocrit and bone marrow examination for diagnosis of polycythemia vera (PV), according to the revised WHO criteria; the search for complementary clonal markers, such as ASXL1, EZH2, IDH1/IDH2, and SRSF2 for the diagnosis of myelofibrosis (MF) in patients who test negative for JAK2V617, CALR or MPL driver mutations.
Activating point mutations in the MPL gene encoding the thrombopoietin receptor are found in 3%-10% of essential thrombocythemia (ET) and myelofibrosis patients.
We screened 136 patients with myelofibrosis and a median age of 58 years who underwent allogeneic stem cell transplantation (AHSCT) for molecular residual disease for JAKV617F (n=101), thrombopoietin receptor gene (MPL) (n=4) or calreticulin (CALR) (n=31) mutation in peripheral blood on day +100 and +180 after AHSCT.
Mutations in Janus Kinase-2 (JAK2), calreticulin (CALR) and myeloproliferative leukemia protein (MPL) genes have been recently associated to MF and they all activate the JAK/STAT signaling pathway.
Conversely, elimination of macrophages expressing MPL by clodronate liposomes reversed the MF phenotype of the murine model, suggesting that fibrocyte differentiation induced by MPL activation contributes to the progression of MF.
A 65-year-old woman with MPL-mutated essential thrombocythemia and progression to myelofibrosis was noted upon routine pretransplant testing to have mixed field reactivity with anti-D and an historic discrepancy in RhD type.
The thrombopoietin receptor (MPL) has been shown to be mutated (MPLW515L) in myelofibrosis and thrombocytosis yet new approaches to treat this disorder are still required.
The objective of the current study was to examine the impact of CALR mutation variant stratified driver mutational status on overall (OS), myelofibrosis-free (MFFS), thrombosis-free, and leukemia-free survival (LFS) in ET; 495 patients (median age 58 years; 61% females) with ET were fully annotated for the their driver mutational status: 321 (65%) harbored JAK2, 109 (22%) CALR, and 12 (2%) MPL mutations and 11% were triple-negative.
Given their diagnostic relevance, it is also beneficial and relatively straightforward to screen JAK2 V617F negative patients for JAK2 exon 12 mutations (in the case of erythrocytosis) or MPL exon 10 mutations (thrombocytosis or myelofibrosis) using appropriate assays.
Induction of myeloproliferative disorder and myelofibrosis by thrombopoietin receptor W515 mutants is mediated by cytosolic tyrosine 112 of the receptor.
Conclusions Patients with familial thrombocytosis caused by a MPL(Ser505Asn) mutation have a high risk of thrombosis and, with aging, develop splenomegaly and bone marrow fibrosis, significantly affecting their life expectancy.
The ability to routinely assess both JAK2 and MPL mutations would be beneficial in the differential diagnosis of unexplained thrombocytosis or myelofibrosis.