Chronic neutrophilic leukemia: 2022 update on diagnosis, genomic landscape, prognosis, and management

The spectrum of Ph-negative disease: CNL and CSF3R-related disorders

Chronic neutrophilic leukemia (CNL) is a very rare myeloid neoplasm characterized by peripheral blood neutrophilia and a hypercellular marrow with increased granulopoiesis. An activating mutation in CSF3R is present in 80% to 90% of cases. CNL displays some biological overlap in terms of clinical presentation and behavior, as well as genetic profile, with several other myeloid neoplasms, particularly myelodysplastic/myeloproliferative neoplasms (MDS/MPN) and other MPN. Distinguishing these related entities can be challenging, requires close attention to peripheral blood and bone marrow morphology, and can be informed by the mutation pattern: CNL is strongly associated with CSF3R mutation, usually lacks JAK2, MPL, or CALR mutations, and, by definition, lacks BCR::ABL1 rearrangement. Pitfalls in diagnosis include subjectivity in assessing neutrophil dysplasia and distinguishing true neoplastic neutrophilia from reactive neutrophilias that may be superimposed upon or occur as a manifestation of the progression of other myeloid neoplasms. Accurate distinction between neutrophilic myeloid neoplasms is important, as it helps guide patient management and may disclose specific genetic lesions amenable to targeted therapy.

Distinct clinical profiles and patient outcomes in aCML and CNL

The classification of atypical chronic myeloid leukemia (aCML) and chronic neutrophilic leukemia (CNL) as a single disease entity remains a topic of debate. To elucidate the characteristics of both entities, this retrospective cohort study was conducted, encompassing 36 cases of aCML and 18 cases of CNL. We discovered that aCML and CNL presented distinct blood counts, genetics, molecular profiles and outcomes. Specifically, hemoglobin levels (P < 0.001) and platelet counts (P < 0.001) were significantly lower in aCML cases than in CNL cases, with no significant difference in mean white blood cells (P = 0.637). The proportion of abnormal karyotypes was higher in aCML cases compared with CNL cases (P = 0.010). Notably, we found that aCML and CNL showed distinct gene expression profiles by transcriptome sequencing technology. The median follow-up duration for the entire cohort was 8 months (rang 0.4 to 36.6 months), and the median overall survival (OS) was significantly shorter in aCML cases (7.3 months, 95%CI 5.4 to 20.5 months) than in CNL cases (median OS not reached). The one-year OS rate for aCML patients was 31.0% (9/29), compared to 92.9% (13/14) for CNL patients. In conclusion, our study supports the notion that aCML and CNL are indeed distinct disease entities characterized by unique hematological features and clinical outcomes.

Hereditary chronic neutrophilic leukemia in a four-generation family without transformation to acute leukemia

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative neoplasm (MPN) characterized by peripheral blood neutrophilia, marrow granulocyte hyperplasia, hepatosplenomegaly, and driver mutations in the colony-stimulating factor 3 receptor (CSF3R). Designation of activating CSF3R mutations as a defining genomic abnormality for CNL has led to increased recognition of the disease. However, the natural history of CNL remains poorly understood with most patients reported being of older age, lacking germline data, and having poor survival, in part due to transformation to acute leukemia. CSF3R driver mutations in most patients with CNL have been reported to be acquired, although rare cases of germline mutations have been described. Here, we report the largest pedigree to date with familial CNL, spanning four generations with affected family members ranging in age from 4 to 53 years, none of whom have transformed to acute leukemia. A heterozygous T618I CSF3R mutation was identified in peripheral blood and mesenchymal stromal cells from the proband and in all affected living family members, while the unaffected family members tested were homozygous wild type. We show that the T618I mutation also confers a survival advantage to neutrophils in an MCL1-dependent manner. Collectively, these data provide additional insights into the natural history of familial CNL arising from T618I CSF3R mutations and suggest that enhanced neutrophil survival also contributes to the high neutrophil count observed in patients with CNL.

Research progress of additional pathogenic mutations in chronic neutrophilic leukemia

Chronic neutrophilic leukemia (CNL) is a rare type of myeloproliferative neoplasm (MPN). Due to its nonspecific clinical symptoms and lack of specific molecular markers, it was previously difficult to distinguish it from other diseases with increased neutrophils. However, the discovery of the CSF3R mutation in CNL 10 years ago and the update of the diagnostic criteria by the World Health Organization (WHO) in 2016 brought CNL into a new era of molecular diagnosis. Next-generation sequencing (NGS) technology has led to the identification of numerous mutant genes in CNL. While CSF3R is commonly recognized as the driver mutation of CNL, other mutations have also been detected in CNL using NGS, including mutations in other signaling pathway genes (CBL, JAK2, NARS, PTPN11) and chromatin modification genes (ASXL1, SETBP1, EZH2), DNA methylation genes (DNMT3A, TET2), myeloid-related transcription factor genes (RUNX1, GATA2), and splicing and RNA metabolism genes (SRSF2, U2AF1). The coexistence of these mutated genes and CSF3R mutations, as well as the different evolutionary sequences of clones, deepens the complexity of CNL molecular biology. The purpose of this review is to summarize the genetic research findings of CNL in the last decade, focusing on the common mutated genes in CNL and their clinical significance, as well as the clonal evolution pattern and sequence of mutation acquisition in CNL, to provide a basis for the appropriate management of CNL patients.

Analysis of CSF3R mutations in atypical chronic myeloid leukemia and other myeloid malignancies

We report a series of patients with CSF3R-mutant (CSF3Rmut) atypical chronic myeloid leukemia (aCML), chronic neutrophilic leukemia (CNL) or other hematologic malignancies. We included 25 patients: 5 aCML and 4 CNL CSF3Rmut patients; 1 aCML, 2 CNL, and 2 myelodysplastic/myeloproliferative neoplasm, not otherwise specified patients without CSF3R mutation; and 11 CSF3Rmut patients with other diseases [8 acute myeloid leukemia (AML), 1 chronic myelomonocytic leukemia (CMML), 1 myelodysplastic syndrome (MDS), and 1 acute lymphoblastic leukemia (ALL)]. Patients with aCML or CNL were tested by Sanger sequencing and pyrosequencing to identify CSF3R T618I. Twenty-two patients underwent gene panel analysis. CSF3R mutations, mostly T618I (8/9), were found at high frequencies in both aCML and CNL patients [5/6 aCML and 4/6 CNL]. Two aCML patients in early adulthood with CSF3R T618I and biallelic or homozygous CEBPA mutations without other mutations presented with increased blasts and exhibited remission for >6 years after transplantation. The other 7 CSF3Rmut aCML or CNL patients were elderly adults who all had ASXL1 mutations and frequently presented with SEBP1 and SRSF2 mutations. Five AML patients had CSF3R exon 14 or 15 point mutations, and 6 other patients (3 AML, 1 CMML, 1 MDS, and 1 ALL) had truncating mutations, demonstrating differences in leukocyte counts and mutation status. In conclusion, CSF3R mutations were found at a higher frequency in aCML patients than in previous studies, which might reflect ethnic differences. Additional studies are needed to confirm these findings and the relationship between CSF3R and CEBPA mutations.

A lasso and random forest model using flow cytometry data identifies primary myelofibrosis

Thrombocythemia (ET), polycythemia vera (PV), primary myelofibrosis (PMF), prefibrotic/early (pre-PMF), and overt fibrotic PMF (overt PMF) are classical Philadelphia-Negative (Ph-negative) myeloproliferative neoplasms (MPNs). Differentiating between these types based on morphology and molecular markers is challenging. This study aims to clarify the application of flow cytometry in the diagnosis and differential diagnosis of classical MPNs. This study retrospectively analyzed the immunophenotypes, clinical characteristics, and laboratory findings of 211 Ph-negative MPN patients, including ET, PV, pre-PMF, overt PMF, and 47 controls. Compared to ET and PV, PMF differed in white blood cells, hemoglobin, blast cells in the peripheral blood, abnormal karyotype, and WT1 gene expression. PMF also differed from controls in CD34+ cells, granulocyte phenotype, monocyte phenotype, percentage of plasma cells, and dendritic cells. Notably, the PMF group had a significantly lower plasma cell percentage compared with other groups. A lasso and random forest model select five variables (CD34+CD19+cells and CD34+CD38- cells on CD34+cells, CD13dim+CD11b- cells in granulocytes, CD38str+CD19+/-plasma, and CD123+HLA-DR-basophils), which identify PMF with a sensitivity and specificity of 90%. Simultaneously, a classification and regression tree model was constructed using the percentage of CD34+CD38- on CD34+ cells and platelet counts to distinguish between ET and pre-PMF, with accuracies of 94.3% and 83.9%, respectively. Flow immunophenotyping aids in diagnosing PMF and differentiating between ET and PV. It also helps distinguish pre-PMF from ET and guides treatment decisions.

CSF3R mutated myeloid neoplasms: Beyond chronic neutrophilic leukemia

CSF3R activating mutation is a genetic hallmark of chronic neutrophilic leukemia (CNL), and is also present in a subset of atypical chronic myeloid leukemia (aCML), but infrequent in other myeloid neoplasms. However, the occurrence of CSF3R mutations in various myeloid neoplasms is not well studied. Here we evaluate the spectrum of CSF3R mutations and the clinicopathologic features of CSF3R mutated myeloid neoplasms. We retrospectively identified CSF3R mutations in a variety of myeloid neoplasms: two CNL, three atypical chronic myeloid leukemia (aCML), nine acute myeloid leukemia (AML), one chronic myelomonocytic leukemia, and one myeloproliferative neoplasm. The prototypic T618I mutation was found in 50% of cases: CNL (2/2), aCML (2/3) and AML (4/9). We observed a new recurrent CSF3R mutation Q776* in 25% of cases, and a potential-germline mutation in a 20-year-old patient. Co-occurring mutations were often in epigenetic modifier and spliceosome. IDH/RUNX1 and tumor suppressor mutations were frequent in AML but absent in CNL/aCML. All CNL/aCML patients succumbed within 2-years of diagnosis. We demonstrate that CSF3R mutations are not restricted to CNL. CNL and aCML show similar clinicopathologic and molecular features, suggesting that CNL may be best classified as myelodysplastic/myeloproliferative neoplasm rather than myeloproliferative neoplasm.

Guide to the Diagnosis of Myeloid Neoplasms: A Bone Marrow Pathology Group Approach

OBJECTIVES

The practicing pathologist is challenged by the ever-increasing diagnostic complexity of myeloid neoplasms. This guide is intended to provide a general roadmap from initial case detection, often triggered by complete blood count results with subsequent blood smear review, to final diagnosis.

METHODS

The integration of hematologic, morphologic, immunophenotypic, and genetic features into routine practice is standard of care. The requirement for molecular genetic testing has increased along with the complexity of test types, the utility of different testing modalities in identifying key gene mutations, and the sensitivity and turnaround time for various assays.

RESULTS

Classification systems for myeloid neoplasms have evolved to achieve the goal of providing a pathology diagnosis that enhances patient care, outcome prediction, and treatment options for individual patients and is formulated, endorsed, and adopted by hematologists/oncologists.

CONCLUSIONS

This guide provides diagnostic strategies for all myeloid neoplasm subtypes. Special considerations are provided for each category of testing and neoplasm category, along with classification information, genetic testing requirements, interpretation information, and case reporting recommendations based on the experience of 11 Bone Marrow Pathology Group members.

Case report: Chronic neutrophilic leukemia associated with monoclonal gammopathies. A case series and review of genetic characteristics and practical management

Chronic neutrophilic leukemia (CNL) is a rare but potentially aggressive BCR::ABL1 negative myeloproliferative neoplasm, characterized by sustained mature, neutrophilic leukocytosis. The discovery of key driver mutations in the colony-stimulating-factor-3 receptor (CSF3R) gene resulted in the updated World Health Organization (WHO) diagnostic criteria in 2016. A significant number of CNL cases have been associated with plasma cell dyscrasias, predominantly multiple myeloma (MM) and monoclonal gammopathy of unknown significance (MGUS). Compared to pure CNL, mutated CSF3R is infrequently reported in CNL cases associated with monoclonal gammopathies (MG). Until now it remains unclear whether CNL and occurring plasma cell neoplasms are clonally related or CNL is developing secondary to the underlying dyscrasia. Owing to its rarity, currently no standard of care management exists for CNL and MG-associated CNL. In this case series we report the multi-center experience of five MG-associated CNL cases with a median age of diagnosis of 69 years. Three patients (66%) showed predominance of lambda light chain expression. Four (80%) eventually evolved to MM, and one CNL-MGUS patient developed secondary acute myeloid leukemia (AML). Mutated CSF3R was present in the patient who developed AML but was absent in other cases. To assess possible associated genetic aberrations we performed recurrent analysis with next-generation sequencing (NGS). Two patients (40%) deceased with a median time of survival of 8 years after CNL diagnosis. Three (60%) are currently in follow-up with no reoccurring leukocytosis. This case series, followed by a short review, provides a long-term clinical and genetic overview of five CNL cases associated with MG.