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Eosinophilia associated with PCM1::JAK2 fusion and classic Philadelphia (Ph)-negative myeloproliferative neoplasms (MPN) are both clonal disorders caused by a dysregulation of the JAK2 signaling pathway. The myeloid neoplasm with t(8;9)(p22;p24.1) and PCM1::JAK2 rearrangement is now formally included among the myeloid/lymphoid neoplasms with eosinophilia (M/LN-eo) and tyrosine kinase fusion genes. To date, no data on genetic predisposition to M/LN-eo with PCM1::JAK2 rearrangement are known, while it is well recognized that a subset of classic Ph-negative MPN segregates within families, suggesting a role for germline predisposition in disease etiology. Here we report the first pedigree with a case of classic Ph-negative MPN and a case of M/LN-eo with PCM1::JAK2 . Our patient carried two acquired molecular abnormalities involving JAK2 gene (PCM1:: JAK2 fusion and JAK2 H531Y) along with a germline mutation ( BLM Y736fs*5, variant allele frequency VAF 41.7%), whereas his sister had the canonical JAK2 V617F driver mutation. This particular pedigree could arise the hypothesis of a genetic predisposition to acquire different JAK2 molecular abnormalities as a maladaptive somatic genetic rescue of an underlying germline predisposition, namely the germline BLM Y736fs*5 mutation.

The authors identified calreticulin mutations in the majority of patients with essential thrombocythemia and myelofibrosis who did not have JAK2 mutations. The mutation alters calreticulin protein, and cells expressing the mutant protein are more responsive to growth factors. Philadelphia chromosome–negative myeloproliferative neoplasms include polycythemia vera, essential thrombocythemia, and primary myelofibrosis. 1 A unique gain-of-function mutation in the Janus kinase 2 gene ( JAK2 ) is found in about three quarters of patients in whom these disease entities have been diagnosed. 2 , 3 The valine-to-phenylalanine (V617F) alteration constitutively activates JAK2, resulting in increased phosphorylation of its substrates and leading to increased cytokine responsiveness of myeloid cells. The JAK2 V617F mutation is present in approximately 95% of patients with polycythemia vera and in 50 to 60% of those with essential thrombocythemia or primary myelofibrosis. 4 In addition, somatic mutations of JAK2 exon 12 . . .

Somatic mutations in splicing factor genes frequently occur in myeloid neoplasms. While SF3B1 mutations are associated with myelodysplastic syndromes (MDS) with ring sideroblasts, SRSF2 P95 mutations are found in different disease categories, including MDS, myeloproliferative neoplasms (MPN), myelodysplastic/myeloproliferative neoplasms (MDS/MPN), and acute myeloid leukemia (AML). To identify molecular determinants of this phenotypic heterogeneity, we explored molecular and clinical features of a prospective cohort of 279 SRSF2 P95 -mutated cases selected from a population of 2663 patients with myeloid neoplasms. Median number of somatic mutations per subject was 3. Multivariate regression analysis showed associations between co-mutated genes and clinical phenotype, including JAK2 or MPL with myelofibrosis (OR = 26.9); TET2 with monocytosis (OR = 5.2); RAS-pathway genes with leukocytosis (OR = 5.1); and STAG2 , RUNX1 , or IDH1/2 with blast phenotype (MDS or AML) (OR = 3.4, 1.9, and 2.1, respectively). Within patients with SRSF2–JAK2 co-mutation , JAK2 dominance was invariably associated with clinical feature of MPN, whereas SRSF2 mutation was dominant in MDS/MPN. Within patients with SRSF2–TET2 co-mutation, clinical expressivity of monocytosis was positively associated with co-mutated clone size. This study provides evidence that co-mutation pattern, clone size, and hierarchy concur to determine clinical phenotype, tracing relevant genotype–phenotype associations across disease entities and giving insight on unaccountable clinical heterogeneity within current WHO classification categories.

Background Pediatric Mastocytosis is a rare and heterogeneous disease, characterized by accumulation of mast cells in the skin (Cutaneous Mastocytosis) and/or, less frequently, in other organs, mainly liver, spleen, bone marrow, lymph nodes and gastrointestinal tract (Systemic Mastocytosis). Patients affected by Systemic Mastocytosis show symptoms caused by  a massive release of mast cell mediators: itching, flushing, abdominal pain, generalized weakness, fatigue and neuropsychiatric disorders. Moreover, children with Systemic Mastocytosis are at greater risk of anaphylactic/anaphylactoid reactions, often poorly controlled by the conventional therapy with antihistamines, mast cells stabilizers and steroids. As a result, children affected by Systemic Mastocytosis have a poor quality of life and suffer the consequence of prolonged steroidal treatment. Case presentation A child with Systemic Mastocytosis and severe symptoms, refractory to symptomatic and steroidal therapy, has been successfully treated with Omalizumab, an anti-IgE monoclonal antibody usually employed in allergic patients with severe asthma and orticaria. The onset of clinical benefit of Omalizumab therapy was extraordinarily rapid, but proved to be strictly dependent on drug administration. The child has become completely and steadily asymptomatic. No other anaphylactic episodes have been reported. Steroid treatment could be definitively withdrawn after the second dose of Omalizumab, and all the other medications were later reduced. Twenty months after beginning, Omalizumab therapy is still ongoing with good symptomatology control; no side effects have been observed so far. Conclusions In our experience, Omalizumab is an effective treatment for children affected by Systemic Mastocytosis not responding to conventional medical treatments. The main strengths of this therapy are its rapid and extraordinary efficacy to control the severe mast cells mediator-related symptoms, the lack of side effects and its steroid-sparing effect. However, more extensive and controlled studies in pediatric patients affected by Systemic Mastocytosis are needed to substantiate these promising findings.

AbstractIntroduction: Acute myeloid leukemia (AML) is a molecularly and clinically heterogeneous disease. Nearly 50% of patients exhibit a normal karyotype, although genomic aberrations are recurrent. Translocations involving JAK2 have increasingly been identified in patients with JAK2V617F-negative myeloproliferative neoplasms, as well as in various other hematologic diseases. Here, we present a unique case of a de novo AML patient with a t(8;9)(p22;p24) translocation, resulting in HMBOX1::JAK2 fusion. Case Presentation: The patient exhibited anemia, leukocytosis, and thrombocytopenia, with bone marrow analysis revealing a significant population of CD34+CD33+ myeloid blasts. The conventional cytogenetic analysis initially showed a normal karyotype, later identifying the t(8;9) translocation after relapse. Molecular characterization of the translocation allowed us to delineate the breakpoints regions, which map to exon 5 of the HMBOX1 gene and exon 19 of the JAK2 gene. The resulting transcript was an in-frame fusion. The patient was diagnosed with acute monocytic leukemia. Induction chemotherapy (cytarabine and idarubicin) initially achieved remission, but subsequent relapses led to the use of venetoclax and 5-azacytidine, which again resulted in remission. Unfortunately, disease progression followed, and the patient ultimately succumbed to AML. Conclusion: This is the first report that molecularly characterizes the HMBOX1::JAK2 fusion in a de novo AML patient. The identification of this novel alteration adds to the growing and heterogeneous molecular landscape of AML and suggests a potential new avenue for targeted therapy.

Patients with myeloproliferative neoplasms (MPN) are known to have higher incidence of nonhematological second primary malignancies (SPM) compared to general population. In the MYSEC study on 781 secondary myelofibrosis (SMF) patients, the incidence of SPM after SMF diagnosis resulted 0.98/100 patient‐years. When including non‐melanoma skin cancers (NMSC), the incidence arose to 1.56/100 patient‐years. In SMF, JAK inhibitor treatment was associated only with NMSC occurrence. Then, we merged the MYSEC cohort with a large dataset of PV and ET not evolving into SMF. In this subanalysis, we did not find any correlation between SPM and SMF occurrence. These findings highlight the need of studies aimed at identifying MPN patients at higher risk of SPM. The incidence of second primary malignancies in postpolycythemia and post thrombocythemia myelofibrosis is around 1/100 patient‐years. There was no evidence of association between JAK inhibitor treatment and second primary malignancies development, with the exception of non‐melanoma skin cancer occurrence. In patients with polycythemia or thrombocythemia, the occurrence of myelofibrosis is not associated to that of second primary malignancies, leaving the two events pathogenetically independent.

In a cohort of 3131 patients with myeloproliferative neoplasms (MPNs), we identified 200 patients (6.4%) who reported a second case of haematological malignancies (HM) in first‐ or second‐degree relatives. The occurrence of a second HM in the family was not influenced by MPN subtype, sex or driver mutation, while it was associated with age at MPN diagnosis: 8.5% of patients diagnosed with MPN younger than 45 years had a second relative affected with HM compared to 5.5% of those diagnosed at the age of 45 years or older (p = 0.003), thus suggesting a genetic predisposition to HM with early onset.

Exome sequencing of primary tumors identifies complex somatic mutation patterns. Assignment of relevance of individual somatic mutations is difficult and poses the next challenge for interpretation of next generation sequencing data. Here we present an approach how exome sequencing in combination with SNP microarray data may identify targets of chromosomal aberrations in myeloid malignancies. The rationale of this approach is that hotspots of chromosomal aberrations might also harbor point mutations in the target genes of deletions, gains or uniparental disomies (UPDs). Chromosome 11 is a frequent target of lesions in myeloid malignancies. Therefore, we studied chromosome 11 in a total of 813 samples from 773 individual patients with different myeloid malignancies by SNP microarrays and complemented the data with exome sequencing in selected cases exhibiting chromosome 11 defects. We found gains, losses and UPDs of chromosome 11 in 52 of the 813 samples (6.4%). Chromosome 11q UPDs frequently associated with mutations of CBL. In one patient the 11qUPD amplified somatic mutations in both CBL and the DNA repair gene DDB1. A duplication within MLL exon 3 was detected in another patient with 11qUPD. We identified several common deleted regions (CDR) on chromosome 11. One of the CDRs associated with de novo acute myeloid leukemia (P=0.013). One patient with a deletion at the LMO2 locus harbored an additional point mutation on the other allele indicating that LMO2 might be a tumor suppressor frequently targeted by 11p deletions. Our chromosome-centered analysis indicates that chromosome 11 contains a number of tumor suppressor genes and that the role of this chromosome in myeloid malignancies is more complex than previously recognized.

To the Editor: In their review of the causes of Budd–Chiari syndrome (BCS), Garcia-Pagán and Valla (April 6 issue) 1 note that myeloproliferative neoplasms are the most frequent underlying condition leading to BCS and therefore recommend testing for driver somatic mutations of JAK2 , CALR , and MPL . In patients with triple-negative myeloproliferative neoplasms, they suggest performing next-generation sequencing, particularly for the detection of mutations with a low allele burden or noncanonical mutations, to improve diagnostic accuracy. 2 Among 2664 patients with myeloproliferative neoplasms in our single-center cohort, BCS was observed in only 16 (0.6%), all of whom had a JAK2 V617F mutation. Given . . .

Among classical BCR-ABL-negative myeloproliferative neoplasms (MPN), primary myelofibrosis (PMF) is the most aggressive subtype from a clinical standpoint, posing a great challenge to clinicians. Whilst the biological consequences of the three MPN driver gene mutations (JAK2, CALR, and MPL) have been well described, recent data has shed light on the complex and dynamic structure of PMF, that involves competing disease subclones, sequentially acquired genomic events, mostly in genes that are recurrently mutated in several myeloid neoplasms and in clonal hematopoiesis, and biological interactions between clonal hematopoietic stem cells and abnormal bone marrow niches. These observations may contribute to explain the wide heterogeneity in patients’ clinical presentation and prognosis, and support the recent effort to include molecular information in prognostic scoring systems used for therapeutic decision-making, leading to promising clinical translation. In this review, we aim to address the topic of PMF molecular genetics, focusing on four questions: (1) what is the role of mutations on disease pathogenesis? (2) what is their impact on patients’ clinical phenotype? (3) how do we integrate gene mutations in the risk stratification process? (4) how do we take advantage of molecular genetics when it comes to treatment decisions?