ICUS/CCUS/CHIP: basics & beyond

Genomic instability and genetic heterogeneity in aging: insights from clonal hematopoiesis (CHIP), monoclonal gammopathy (MGUS), and monoclonal B-cell lymphocytosis (MBL)

Aging is a multifaceted process characterized by a gradual decline in physiological function and increased susceptibility to a range of chronic diseases. Among the molecular and cellular mechanisms driving aging, genomic instability is a fundamental hallmark, contributing to increased mutation load and genetic heterogeneity within cellular populations. This review explores the role of genomic instability and genetic heterogeneity in aging in the hematopoietic system, with a particular focus on clonal hematopoiesis of indeterminate potential (CHIP), monoclonal gammopathy of undetermined significance (MGUS), and monoclonal B-cell lymphocytosis (MBL) as biomarkers. CHIP involves the clonal expansion of hematopoietic stem cells with somatic mutations. In contrast, MGUS is characterized by the presence of clonal plasma cells producing monoclonal immunoglobulins, while MBL is characterized by clonal proliferation of B cells. These conditions are prevalent in the aging population and serve as measurable indicators of underlying genomic instability. Studying these entities offers valuable insights into the mechanisms by which somatic mutations accumulate and drive clonal evolution in the hematopoietic system, providing a deeper understanding of how aging impacts cellular and tissue homeostasis. In summary, the hematopoietic system serves as a powerful model for investigating the interplay between genomic instability and aging. Incorporating age-related hematological conditions into aging research, alongside other biomarkers such as epigenetic clocks, can enhance the precision and predictive power of biological age assessments. These biomarkers provide a comprehensive view of the aging process, facilitating the early detection of age-related diseases and hopefully enabling personalized healthcare strategies.

The utility of a myeloid mutation panel for the diagnosis of myelodysplastic syndrome and myelodysplastic/myeloproliferative neoplasm

INTRODUCTION

The diagnosis of myelodysplastic syndromes (MDS) and myelodysplastic/myeloproliferative neoplasms (MDS/MPN) is based on morphology and cytogenetics/FISH findings per 2017 WHO classification. With rare exceptions, somatic mutations have not been incorporated as the diagnostic criteria.

METHODS

We analyzed the utility of mutational analysis with a targeted 54-gene or 40-gene next-generation sequencing (NGS) panel in the diagnosis of MDS and MDS/MPN.

RESULTS

We retrospectively collected 92 patients who presented with unexplained cytopenia with or without cytosis, including 32 low-grade MDS (MDS-L), 18 high-grade MDS (MDS-H), 5 therapy-related MDS (MDS-TR), 19 MDS/MPN, and 18 negative cases. Of 92 patients, 197 somatic mutations involving 38 genes were detected and had variant allele frequency (VAF) ranging from 3% to 99%. The most common mutated genes were TET2, ASXL1, RUNX1, TP53, SRSF2, and SF3B1. MDS-L, MDS-H, MDS-TR, and MDS/MPN showed an average number of somatic mutations with a mean VAF of 1.9/33%, 2.6/30%, 2/36%, and 4/41%, respectively. SF3B1 mutations were exclusively observed in MDS-L and MDS/MPN. TP53 gene mutations were more frequently seen in MDS-H and MDS-TR. Among 34 patients with a diagnosis of MDS or MDS/MPN with normal cytogenetics, 31 patients (91%) had at least 1 mutation and 24 patients (71%) had ≥2 mutations with ≥10% VAF.

CONCLUSION

A myeloid mutational panel provides additional evidence of clonality besides cytogenetics/FISH studies in the diagnosis of cytopenia with or without cytosis. Two or more mutations with ≥10% VAF highly predicts MDS and MDS/MPN with a positive predictive value of 100%.

What to tell your patient with clonal hematopoiesis and why: insights from 2 specialized clinics

Acquired genetic mutations in hematopoietic stem or progenitor cells can lead to clonal expansion and imbalanced blood cell production. Clonal hematopoiesis is exceptionally common with human aging, confers a risk of evolution to overt hematologic malignancy, and increases all-cause mortality and the risk of cardiovascular disease. The degree of risk depends on the specific mutant allele driving clonal expansion, number of mutations, mutant allele burden, and concomitant nongenetic risk factors (eg, hypertension or cigarette smoking). People with clonal hematopoiesis may come to clinical attention in a variety of ways, including during the evaluation of a possible hematologic malignancy, as an incidental discovery during molecular analysis of a nonhematologic neoplasm, after hematopoietic cell transplantation, or as a result of germline testing for inherited variants. Even though the risk of clonal progression or a cardiovascular event in an individual patient with clonal hematopoiesis may be low, the possibility of future clinical consequences may contribute to uncertainty and worry, because it is not yet known how to modify these risks. This review summarizes clinical considerations for patients with clonal hematopoiesis, including important points for hematologists to consider discussing with affected persons who may understandably be anxious about having a mutation in their blood that predisposes them to develop a malignancy, but which is significantly more likely to result in a myocardial infarction or stroke. The increasing frequency with which people with clonal hematopoiesis are discovered and the need for counseling these patients is driving many institutions to create specialized clinics. We describe our own experience with forming such clinics.

Nonclonal chromosomal alterations and poor survival in cytopenic patients without hematological malignancies

Background

Clonal chromosomal alterations (CCAs) reflect recurrent genetic changes derived from a single evolving clone, whereas nonclonal chromosomal alterations (NCCAs) comprise a single or nonrecurrent chromosomal abnormality. CCAs and NCCAs in hematopoietic cells have been partially investigated in cytopenic patients without hematological malignancies.

Methods

This single-center retrospective study included 253 consecutive patients who underwent bone marrow aspiration to determine the cause of cytopenia between 2012 and 2015. Patients with hematological malignancies were excluded. CCA was defined as a chromosomal aberration detected in more than two cells, and NCCA was defined as a chromosomal aberration detected in a single cell.

Results

The median age of the patients was 66 years. There were 135 patients without hematological malignancies (median age, 64 years; 69 females); of these, 27 patients (median age, 69 years; 8 females) harbored chromosomal abnormalities. CCAs were detected in 14 patients; the most common CCA was −Y in eight patients, followed by inv.(9) in three patients and mar1+, inv. (12), and t (19;21) in one patient each. NCCAs were detected in 13 patients; the most frequent NCCA was +Y in four patients, followed by del (20), + 8, inv. (2), − 8, and add (6) in one patient each. Moreover, nonclonal translocation abnormalities, including t (9;14), t (14;16), and t (13;21), were observed in three patients. One patient had a complex karyotype in a single cell. The remaining 106 patients with normal karyotypes comprised the control group (median age, 65 years; range, 1–92 years; 56 females). Further, follow-up analysis revealed that the overall survival of the NCCA group was worse than that of the CCA and the normal karyotype groups (P < 0.0001; log-rank test).

The survival of the NCCA-harboring cytopenic patients was worse than that of the CCA-harboring cytopenic patients without hematological malignancies, suggesting that follow-up should be considered for both CCA- and NCCA-harboring cytopenic patients.

Unexplained chronic cytopenia: is it idiopathic cytopenia of undetermined significance or myelodysplastic syndrome

Idiopathic cytopenia is a condition where there is a decrease in peripheral blood counts causing either anaemia, leucopoenia and thrombocytopaenia. Most cases of cytopenia reveal a cause on further workup. But very rarely, in some cases, a definitive cause could not be identified. Unexplained cytopenia becomes challenging and poses difficulty in diagnosis and management. Discriminating these groups of bone marrow failure disorders from myelodysplastic syndrome (MDS) becomes an important clinical question. We describe a case of a middle-aged Hispanic woman who presented with pancytopenia and on extensive workup did not reveal any specific cause. Her bone marrow examination revealed severely reduced megakaryocytes but with normal haemopoiesis of other lineages. Cytogenetics, flow cytometry, comprehensive next-generation whole genomic analysis did not reveal any abnormalities. She fit the criteria for idiopathic cytopenia of undetermined significance rather than MDS. She remained asymptomatic and her counts never improved with immunosuppressives or thrombopoietin mimetics.

Diagnostic Value of Flow Cytometry Standardized Using the European LeukemiaNet for Myelodysplastic Syndrome

BACKGROUND

Myelodysplastic syndromes (MDS) and idiopathic cytopenia of undetermined significance (ICUS) are heterogeneous hematological disorders characterized by hematopoietic dysplasia and/or chromosomal aberrancy.

OBJECTIVES

This study aimed to evaluate the diagnostic value of flow cytometry standardized using the European LeukemiaNet (ELN) for MDS and ICUS by analyzing samples obtained from patients with cytopenia based on morphological examination, cytogenetic analysis, and flow cytometry.

METHODS

We retrospectively analyzed bone marrow samples aspirated from 253 consecutive patients (median age: 66 years [range: 1-92]) to identify the cause of cytopenia.

RESULTS

Sixty patients presented with MDS, and 16 with ICUS. MDS subtypes were distributed as follows: MDS with single-lineage dysplasia (n = 10); MDS with multi-lineage dysplasia (n = 10); MDS with ringed sideroblasts (n = 4); MDS with excess blasts-1 (n = 9); MDS with excess blasts-2 (n = 13), MDS unclassified (n = 5); 5q-syndrome (n = 6); and MDS/myeloproliferative neoplasms (n = 3). Four representative ELN indexes were used. Two or more ELN MDS indexes were in the abnormal range in 35 MDS cases (58.3%) and 4 ICUS cases (25.0%).

CONCLUSIONS

Morphological examination remains the standard for MDS diagnosis. Considering the low incidence of genetically proven ICUS (20.2-27.5%), the low sensitivity of ELN MDS indexes for ICUS is considered a valuable alternative.

Cyclin D1 expression and novel mutational findings in Rosai-Dorfman disease

Rosai-Dorfman disease (RDD) is an enigmatic histiocytic disorder classically diagnosed by a distinctive combination of pathological features: emperipolesis, or migration of intact haematological cells through the voluminous cytoplasm of lesional histiocytes, and expression of S100 by these histiocytes. The pathogenesis has long been elusive until the recent detection of recurrent and mutually exclusive mutations in several oncogenes in the mitogen-activated protein kinase (MAPK) pathway. Based on these findings, we investigated a cohort of 21 RDD patients and found that the lesional histiocytes in 86% (18/21) of patients exhibited strong and diffuse nuclear Cyclin D1 expression, which not only may provide a diagnostic marker for this sometimes pathologically challenging disease, but also probably reflects constitutive MAPK pathway activation because we additionally identified phosphorylated-ERK expression in 90% (19/21) of cases. Further, we performed massively parallel sequencing on a subset (6/18) of the CyclinD1 positive cases, identifying several mutations that have not been previously reported in RDD. Taken together, our findings bolster the concept of RDD as a disease of MAPK activation in a substantial percentage of cases and enhance the current understanding of the pathogenesis of RDD.

Replicative senescence of hematopoietic cells in patients with idiopathic cytopenia of undetermined significance

We hypothesized that a subset of idiopathic cytopenia of undetermined significance (ICUS) is associated with an increased autonomous proliferation with exhaustion of hematopoiesis. The aim of this study was to investigate the cell turnover rate and replicative history of the bone marrow cells of ICUS patients. To this end, we examined telomere length (TL), proliferation, and apoptosis of the bone marrow cells of ICUS patients and healthy controls (HCs) using telomere quantitative fluorescence in situ hybridization and immunohistochemical staining for Ki-67 and cleaved caspase-3. We also performed targeted sequencing of 88 myeloid-associated genes. A total of 37 patients with ICUS were enrolled in this study, with a median age of 66 years (range: 31-83). TLs were significantly shorter in patients with ICUS than in the HCs (8.8, interquartile range [IQR] 6.8-12.1 vs 18.4, IQR 14.4-22.0, p < 0.0001). Proliferation (Ki-67-positive) and apoptosis (cleaved caspase-3-positive) were significantly increased in patients with ICUS compared to HCs (median = 20.0% vs 5.0%, p = 0.0003; 45.0% vs 22.5%, p = 0.0005, respectively). The shortening of TL and the increased proliferation and apoptotic activity was also prominent in patients with ICUS without mutation and dysplasia than in HCs (p < 0.0001, p < 0.0001, and p = 0.0093, respectively). TL was not associated with mutational profile and clinical characteristics as well in patients with ICUS. To our knowledge, this is the first study to show that ICUS is associated with premature replicative senescence with increased proliferation and apoptosis of bone marrow cells. Further study is needed to address the cause of replicative exhaustion in ICUS patients.

The Progress of Next Generation Sequencing in the Assessment of Myeloid Malignancies

The introduction and advances on next-generation sequencing have led to novel ways to integrate simultaneous assessment of multiple target genes in routine laboratory analysis. Assessment of myeloid neoplasms with targeted next-generation sequencing panels shows evidence to improve diagnosis, assist therapeutic decisions, provide better information about prognosis, and better detection of minimal residual disease. Herein, we provide information for application and utilization of next-generation sequencing studies with a focus on the most important mutations in acute myeloid leukemia, myelodysplastic syndrome, myeloproliferative neoplasms, and other myelodysplastic / myeloproliferative neoplasms in order to integrate them into the daily clinical practice.