Primary thrombocythemia and primary myelofibrosis are common types of myeloproliferative neoplasms (MPNS).Mutational activation of Janus kinase 2 (JAK2) is associated with 50%-60% of MPN events; the underlying cause of approximately 30% of MPN events remains unknown. Recently, a study claimed that mutations in calreticulin (CALR) occur in the majority of MPN patients with JAK2 inactivation (JAK2-disease). Researchers in the study completed whole-exome sequencing of matched samples from six patients with primary myelofibrosis, which led to the discovery that CALR mutations were present in all of the tumor samples. Two of the samples were deleted in exon 9 (a 52bp deletion categorized as a type 1 mutation), and four samples had a 5bp insertion in exon 9 (a type 2 mutation). In addition, CALR-mutated patients, including those from an additional cohort, had both JAK2- and CALR mutations in 88% of JAK2-MPN. Overall, the researchers identified 36 different CALR mutations (mostly type 1 and type 2 mutations), all of which led to a code-shifted alternative reading frame 1, which is predicted to be able to alter the carboxy-terminal structural domain. type 1 mutations are greatly associated with primary myelofibrosis, which implies that the two types of mutations may have different effects. Ectopic expression of a class of 1-mutant proteins confers interleukin-3 (IL-3) toward cell-independent growth, which appears to result from the activation of JAK-signaling sensors and catalysts of transcription 5 (STAT5) signaling. Overall, the authors investigated 1,215 patients with primary thrombocythemia or primary myelofibrosis; 23.5% of these patients had CALR mutations, and patients with CALR+ disease had longer overall survival compared to those with JAK2+ disease. In addition, the researchers completed whole-exome sequencing of an additional 151 MPN samples and found CALR exon 9 insertions and deletions in 26 of 31 patients with JAK2-primary thrombocythemia or primary myelofibrosis; similar results were found in a larger population. type 1 and type 2 mutations were the most common, with type 1 mutations being the most common in primary myelofibrosis samples were the most common. Interestingly, these findings suggest that CALR+ primary thrombocythemia has a higher incidence of transformation to myelofibrosis compared to JAK2+ disease. Additional analyses also showed that the CALR mutation occurred in the hematopoietic stem cell compartment and that it was an early event in the five patients who underwent the experiment, meaning it may be a driver mutation. The researchers identified 19 different CALR mutations, and they also predicted that each mutation affected the carboxy-terminal structural domain. These mutations were predicted to result in the deletion of a KDEL motif, which is able to localize in the endoplasmic reticulum and variably affect the acidity of this structural domain. However, ectopic expression of type 1 and type 2 CALR mutations in HEK293T cells revealed that the subcellular localization of CALR was not affected by the mutations, and therefore, further studies are needed to determine why type 1 and type 2 mutations in CALR are oncogenic. In summary, these papers were added to the list of potential causes of MPN alterations. It will be interesting to discover if these alterations have any impact on treatment. The CALR gene may become a new molecular marker for MPN LBA-1 study: the most common genetic alteration in myeloproliferative neoplasms (MPN) is the JAK2 V617F mutation, seen in 95% of true erythrocytosis (PV), and 50% to 60% of primary thrombocythemia (ET) or primary myelofibrosis (PMF). mutations in exon 12 of JAK2 and platelet receptor (MPL) gene mutations are seen in another 5% to 10% of patients. Specific molecular markers are lacking for the approximately 40% of patients with wild-type JAK2 and MPL ET and PMF. Klampfl Thorsten, MD, PhD, of the Center for Molecular Medicine at the Austrian Academy of Sciences, applied whole-exon gene sequencing to detect reproducible insertions and deletions of the CALR gene, which encodes the calreticulin protein, in PMF patients with wild-type JAK2 and MPL. The investigators then screened 1107 MPN patients for insertion and/or deletion mutations in exon 9 of the CALR gene; no mutations were detected in PV patients, and the CALR mutations all occurred in ET (67%) and PMF (88%) patients with wild-type JAK2 and MPL. In addition, the investigators did not detect CALR exon 9 gene mutations in 254 primary acute myeloid leukemia (AML), 45 chronic myeloid leukemia (CML), 73 myelodysplastic syndromes (MDS), and 64 chronic granulomonocytic leukemia. Patients with ET and PMF with CALR mutations tended to have lower white blood cell counts and higher platelet counts than those with JAK2 mutations. Regardless of ET or PMF, CALR mutants had better overall survival (OS) than JAK2 mutants. ET patients with CALR mutations had a lower incidence of thrombosis than those with JAK2 mutations. Therefore, CALR mutations are specific molecular markers for JAK2 and MPL mutation-negative MPN patients, and their clinical application will improve the diagnosis of the disease and provide a basis for treatment selection. LBA-2 study: Researchers from the UK Cancer Genome Project used exome/genome sequencing to assess CALR gene status in 3,412 samples, and exome sequencing of 151 samples from MPN patients revealed that the majority (26/31) of MPN patients without JAK2 or MPL mutations had somatic mutations in CALR. Whereas CALR and JAK2 and MPL mutations could not coexist, only one of these 3 mutations was present in 97% of patients. In a subsequent expanded study (1,345 patients with hematologic malignancies, 1,517 patients with other tumors, and 550 normal controls), the investigators found that CALR mutations were present in 71% of patients with ET, 56% of patients with PMF, 86% of patients with myelofibrosis after ET, and 8% of patients with MDS, whereas in other myeloid, lymphoid, or solid tumors, the mutations were negative for CALR. CALR mutations were also found in highly purified hematopoietic stem/progenitor cells from five patients with MPN, and thus this mutation may be the driving mutation responsible for the disease. Comment MPN is a group of common hematologic diseases with increasing incidence year by year, and the age of onset is progressively younger, making it imperative to improve the diagnosis and individualized treatment of these diseases. However, compared with other hematologic malignancies, the research progress in this field in recent years has been less significant, except for the fact that JAK2 and MPL mutations have become important molecular markers, which have improved the diagnosis of some MPNs, and specific molecular markers have not been found in nearly half of ETs and PMFs. The results of these two studies were very groundbreaking and aroused strong interest from the participating experts. A sequencing screen identified a somatic mutation in the endoplasmic reticulum molecular chaperone CALR in the majority of wild-type JAK2 MPN patients. While calreticulin is the major calcium-binding protein in the endoplasmic reticulum, it is involved in the regulation of apoptosis, adhesion, immunity and other processes by assisting in the correct folding of proteins and maintenance of cellular calcium homeostasis. mutations in CALR lead to the production of a new C-terminus of the protein, which leads to changes in the function of the protein. In transfected cell lines, aggregation of calreticulin at the Golgi or cell surface is reduced. These results provide new ideas for unraveling the pathogenesis of JAK2 mutation-negative MPN patients, and more studies are needed to confirm the role and significance of CALR mutations in the pathogenesis of MPN. In addition, studies have confirmed that CALR mutations are mainly found in JAK2 and MPL mutation-negative MPN, and CALR mutations are expected to further improve the diagnosis of MPN, and due to their special clinical significance, they may provide an important basis for the individualized treatment of MPN and eventual targeted therapeutic research. Mutations in calreticulin and myeloproliferative neoplasms Primary thrombocythemia and primary myelofibrosis are common types of myeloproliferative neoplasms (MPNS) Mutational activation of Janus kinase 2 (JAK2) is associated with 50-60% of MPN events; the underlying cause of approximately 30% of MPN events remains unknown. Two papers now say that mutations in calreticulin (CALR) occur in the majority of MPN patients with JAK2 inactivation (JAK2-disease). Klampfl et al. completed whole-exome sequencing of matched samples from six patients with primary myelofibrosis, and in turn found that CALR mutations were present in all of the tumor samples. Two of the samples were deleted in exon 9 (a 52bp deletion categorized as a type 1 mutation), and four samples had a 5bp insertion in exon 9 (type 2 mutations). In addition, CALR-mutated patients, including those from an additional cohort, had both JAK2- and CALR mutations in 88% of JAK2-MPN. Overall, Klampfl et al. identified 36 different CALR mutations (mostly type 1 and type 2 mutations), all of which led to a code-shifted alternative reading frame 1, which is predicted to be able to alter the carboxy-terminal structural domain. type 1 mutations are greatly associated with primary myelofibrosis, which means that the two types of mutations may have different effects. Ectopic expression of a class of 1-mutant proteins confers interleukin-3 (IL-3) toward cell-independent growth, which appears to result from the activation of JAK-signaling sensors and catalysts of transcription 5 (STAT5) signaling. Overall, the authors investigated 1,215 patients with primary thrombocythemia or primary myelofibrosis; 23.5% of these patients had CALR mutations, and patients with CALR+ disease had longer overall survival compared to those with JAK2+ disease. In another paper, Nangalia et al. completed whole exome sequencing of 151 MPN samples and found CALR exon 9 insertions and deletions in 26 of 31 patients with JAK2-primary thrombocythemia or primary myelofibrosis; similar results were found in a larger population. type 1 and type 2 mutations were the most common and type 1 mutations were again found in primary myelofibrosis patients. type 1 mutations were in turn most common in primary myelofibrosis samples. Interestingly, these authors found that CALR+ primary thrombocythemia had a higher incidence of transformation to myelofibrosis compared to JAK2+ disease. Additional analyses also showed that the CALR mutation occurred in the hematopoietic stem cell compartment and that it was an early event in the five patients who underwent the experiment, implying that it may be a driver mutation. Nangalia et al. identified 19 different CALR mutations, and they also predicted that each mutation affected the carboxy-terminal structural domain. These mutations were predicted to result in a deletion of a KDEL motif, which is able to localize in the endoplasmic reticulum and variably affect the acidity of this structural domain. However, ectopic expression of type 1 and type 2 CALR mutations in HEK 293T cells revealed that the subcellular localization of CALR was not affected by the mutations, and therefore, further studies are needed to determine why type 1 and type 2 mutations in CALR are oncogenic. In summary, these papers were added to the list of potential causes of MPN alterations. It will be interesting to discover if these alterations have any impact on treatment