Molecular Testing in Patients with Suspected Myelodysplastic Syndromes

The diagnostic utility of targeted gene panel sequencing in discriminating etiologies of cytopenia

The diagnostic utility of somatic mutations in the context of cytopenias is unclear: clonal hematopoiesis can be found in healthy individuals, patients with aplastic anemia (AA), clonal cytopenia of undetermined significance (CCUS) and myelodysplastic syndrome (MDS). We examined a cohort of 207 well-characterized cytopenic patients with a 640-gene next generation sequencing (NGS) panel and compared its diagnostic utility with a "virtual" 41 gene panel. The TET2, SF3B1, ASXL1, and TP53 were the most commonly mutated genes (frequency > 10%). Mutations in the 640-gene panel show high sensitivity (98.3%) but low specificity (47.6%) for diagnosis of MDS. Notably, mutations of splicing factors and genes in the RAS pathway are relatively specific to MDS. Furthermore, high variant allele frequency (VAF) predicts MDS: when the VAF is set at 20%, the positive predictive value (PPV) for MDS is 95.9%, with a specificity of 95.3%. The presence of two or more somatic mutations with ≥10% VAF showed a PPV of 95.2%. While the "virtual" 41-gene panel showed a mild decrease in sensitivity (95.7% vs 98.3%), 100% specificity was observed when either VAF was set at ≥20% (100% vs 95.3%), or two or more somatic mutations had VAFs ≥ 10%. Our study shows targeted gene panel sequencing improves the diagnostic approach and accuracy for unexplained cytopenia, with its high sensitivity and high PPV for MDS when applying VAF cutoffs. Furthermore, a 41-gene panel was shown to have at least comparable performance characteristics to the large 640-gene panel.

Getting personal with myelodysplastic syndromes: is now the right time?

INTRODUCTION

Commonly used scoring systems rely on blood counts, histological and cytological examination of bone marrow and peripheral blood as well as cytogenetic assessments to estimate prognosis of patients with myelodysplastic syndromes (MDS) and guide therapy decisions. Next-generation sequencing (NGS) has identified recurrent genetic abnormalities in up to 90% of patients with MDS and may provide important information regarding the pathogenesis of the disease, diagnostic and prognostic evaluation, and therapy selection. Areas covered: Herein, the authors review the role of NGS in diagnosis, treatment, and prognosis of MDS at various disease stages, and discuss advantages and caveats of incorporating molecular genetics in routine management of MDS. While a vast majority of patients harbor recurrent mutations implicated in MDS pathogenesis, similar mutations can be detected in otherwise healthy individuals with other hematologic malignancies. Besides establishing a diagnosis, NGS may be used to monitor minimal residual disease following treatment. Expert opinion: As more targeted therapies become available, assessment of genetic mutations will become central to individualized therapy selection and may improve diagnostic accuracy and further guide management for each patient. However, multiple challenges remain before NGS can be incorporated into routine clinical practice.

How I use molecular genetic tests to evaluate patients who have or may have myelodysplastic syndromes

Myelodysplastic syndromes (MDS) can be difficult to diagnose, especially when morphological changes in blood and marrow cells are minimal, myeloblast proportion is not increased, and the karyotype is normal. The discovery of >40 genes that are recurrently somatically mutated in MDS patients raised hope that molecular genetic testing for these mutations might help clarify the diagnosis in ambiguous cases where patients present with cytopenias and nondiagnostic marrow morphological findings. However, many older healthy individuals also harbor somatic mutations in leukemia-associated driver genes, especially in DNMT3A, TET2, and ASXL1, and detection of common aging-associated mutations in a cytopenic patient can cause diagnostic uncertainty. Despite this potential confounding factor, certain somatic mutation patterns when observed in cytopenic patients confer a high likelihood of disease progression and may allow a provisional diagnosis of MDS even if morphologic dysplasia and other diagnostic criteria are absent. A subset of acquired mutations also influences risk stratification of patients with an established MDS diagnosis and can inform treatment selection. Many unanswered questions remain about the implications of specific mutations, and clinicians also vary widely in their comfort with interpreting sequencing results. Here, I review the use of molecular genetic assays in patients with possible MDS or diagnosed MDS.