In >95% of cases, mutations that drive the development of an MPN phenotype occur in a mutually exclusive manner in 1 of 3 genes: <i>JAK2</i>, <i>CALR</i>, or <i>MPL</i> The thrombopoietin receptor, MPL, is the key cytokine receptor in MPN development, and these mutations all activate MPL-JAK-STAT signaling in MPN stem cells.
Mutations in JAK2, MPL and CALR genes have been identified in the majority of myeloproliferative neoplasm (MPN) patients, and patients negative for these three mutations are the so-called triple-negative (TN) MPN.
PNA-based FMCA for detecting common JAK2, MPL, and CALR mutations is a rapid, simple, and sensitive technique in BCR-ABL1-negative MPNs with >10% mutant allele at the time of initial diagnosis.
Moreover, the combination of BMN673, ruxolitinib, and hydroxyurea was highly effective in vivo against JAK2(V617F)<sup>+</sup> murine MPN-like disease and also against JAK2(V617F)<sup>+</sup>, CALR(del52)<sup>+</sup>, and MPL(W515L)<sup>+</sup> primary MPN xenografts.
Genomic DNA from peripheral blood, bone marrow, and FFPE bone marrow clot preparations from 52 MPN specimens with known JAK2 and MPL mutation status and 29 non-MPN specimens was analyzed.
Considering these results, we propose that mutant CALR promotes myeloproliferative neoplasm development by activating c-MPL and its downstream pathway.
Mutations in CALR (calreticulin) have been discovered in 50% to 80% of JAK2 (Janus kinase 2) and MPL (myeloproliferative leukemia protein) wild-type patients with Philadelphia-negative myeloproliferative neoplasm (MPNs).
We retrospectively examined the clinical and biological characteristics of 13 patients with concomitant CLL and MPN--eight primary myelofibrosis (PMF), three essential thrombocytosis (ET), and two polycythemia vera (PV)--who presented to our institution between 1998 and 2014, and tested all patients for MPN-specific aberrations, such as JAK2, MPL and CALR mutations.
CALR mutations are identified in about 30% of JAK2/MPL-unmutated myeloproliferative neoplasms (MPNs) including essential thrombocythemia (ET) and primary myelofibrosis.
Discovery in 2006 of mutants of thrombopoietin receptor (TPO-R/MPL) and later on of mutants in negative regulators of JAK-STAT pathway led to the notion that persistent JAK2 activation is a hallmark of MPNs.
Four main molecular types of clonal MPN can be distinguished: JAK2(V617F)-positive ET and PV; JAK2 wild-type ET carrying the MPL(515); mutations in the calreticulin (CALR) gene in JAK2/MPL wild-type ET and MF, and a small proportion of JAK2/MPL/CALR wild-type ET and MF patients.
Somatic mutations in the CALR gene were recently discovered in a substantial proportion of Philadelphia-negative chronic myeloproliferative neoplasm (cMPN) patients lacking JAK2 and MPL mutations.
Recent advances in the biology of MPNs have greatly facilitated their molecular diagnosis since most patients present with mutation(s) in the JAK2, MPL, or CALR genes.
The identification of JAK2/MPL mutations in patients with myeloproliferative neoplasms (MPN) has led to the clinical development of JAK kinase inhibitors, including ruxolitinib.
In total, 199 patients with MPN (54 primary myelofibrosis [PMF], 79 essential thrombocythemia [ET], 58 polycythemia vera [PV], and eight MPN-unclassifiable [MPN-U]) and 4 patients with acute panmyelosis with myelofibrosis (APMF) were retrospectively subjected to Sanger sequencing for CALR, JAK2, and MPL.
Concurrence of B-lymphoblastic leukemia and myeloproliferative neoplasm with copy neutral loss of heterozygosity at chromosome 1p harboring a MPLW515S mutation.
Somatic CALR exon 9 mutations have recently been identified in patients with JAK2/MPL-unmutated myeloproliferative neoplasm, and have become an important clonal marker for the diagnosis of essential thrombocythemia (ET) and primary myelofibrosis.
Recently, germline mutations in Janus kinase 2 (JAK2) and MPL, two genes frequently mutated in sporadic MPD, have been shown to cause inherited thrombocytosis.
The recent discovery of CALR mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients without JAK2/MPL mutations has emerged as a relevant finding for the molecular diagnosis of these myeloproliferative neoplasms (MPN).