Tumor mutational burden (TMB) represents a new determinant of clinical benefit from immune checkpoint blockade that identifies responders independent of PD‐L1 expression levels and is currently being ...explored in clinical trials. Although TMB can be measured directly by comprehensive genomic approaches such as whole‐genome and exome sequencing, broad availability, short turnaround times, costs and amenability to formalin‐fixed and paraffin‐embedded tissue support the use of gene panel sequencing for approximating TMB in routine diagnostics. However, data on the parameters influencing panel‐based TMB estimation are limited. Here, we report an extensive in silico analysis of the TCGA data set that simulates various panel sizes and compositions. We demonstrate that panel size is a critical parameter that influences confidence intervals (CIs) and cutoff values as well as important test parameters including sensitivity, specificity, and positive predictive value. Moreover, we evaluate the Illumina TSO500 panel, which will be made available for TMB estimation, and propose dynamic, entity‐specific cutoff values based on current clinical trial data. Optimizing the cost–benefit ratio, our data suggest that panels between 1.5 and 3 Mbp are ideally suited to estimate TMB with small CIs, whereas smaller panels tend to deliver imprecise TMB estimates for low to moderate TMB (0–30 muts/Mbp), connected with insufficient separation of hypermutated tumors from non‐hypermutated tumors.
What's new?
While the immune system can fight cancer, tumor clones may hijack the body's own mechanisms of dampening immune responses by expressing immune‐checkpoint proteins. Tumor mutational burden (TMB) is an emerging selection biomarker for patients who would benefit from immune checkpoint inhibitor therapy. Unification of TMB estimation and driver mutation detection in a single panel sequencing assay is highly desirable but challenging, however. Combinatorial calculations and simulations in the TCGA dataset show that panel sizes greater than 1.5 Mbp are recommendable, and–although not immunogenic–synonymous and nonsense mutations can be included in TMB estimation together with cancer‐type specific correction factors.
Assessment of Tumor Mutational Burden (TMB) for response stratification of cancer patients treated with immune checkpoint inhibitors is emerging as a new biomarker. Commonly defined as the total ...number of exonic somatic mutations, TMB approximates the amount of neoantigens that potentially are recognized by the immune system. While whole exome sequencing (WES) is an unbiased approach to quantify TMB, implementation in diagnostics is hampered by tissue availability as well as time and cost constrains. Conversely, panel‐based targeted sequencing is nowadays widely used in routine molecular diagnostics, but only very limited data are available on its performance for TMB estimation. Here, we evaluated three commercially available larger gene panels with covered genomic regions of 0.39 Megabase pairs (Mbp), 0.53 Mbp and 1.7 Mbp using i) in silico analysis of TCGA (The Cancer Genome Atlas) data and ii) wet‐lab sequencing of a total of 92 formalin‐fixed and paraffin‐embedded (FFPE) cancer samples grouped in three independent cohorts (non‐small cell lung cancer, NSCLC; colorectal cancer, CRC; and mixed cancer types) for which matching WES data were available. We observed a strong correlation of the panel data with WES mutation counts especially for the gene panel >1Mbp. Sensitivity and specificity related to TMB cutpoints for checkpoint inhibitor response in NSCLC determined by wet‐lab experiments well reflected the in silico data. Additionally, we highlight potential pitfalls in bioinformatics pipelines and provide recommendations for variant filtering. In summary, our study is a valuable data source for researchers working in the field of immuno‐oncology as well as for diagnostic laboratories planning TMB testing.
What's new?
Tumor mutational burden (TMB) is an emerging biomarker to predict response to immune checkpoint inhibitors. While TMB can be measured by whole exome sequencing (WES), costs, turn‐around time, and tissue availability currently favor a panel sequencing approach using FFPE tissue for routine diagnostics. However, performance remains to be clarified. Our study is the first worldwide that analyses three major commercial gene panels by comparing TMB approximation across panels as well as against the technical reference standard WES. The data suggest that TMB approximation using gene panel sequencing of FFPE tumor tissue is feasible and can be implemented in routine diagnostics.
Tyrosine kinase inhibitors currently confer the greatest survival gain for nonsmall cell lung cancer (NSCLC) patients with actionable genetic alterations. Simultaneously, the increasing number of ...targets and compounds poses the challenge of reliable, broad and timely molecular assays for the identification of patients likely to benefit from novel treatments. Here, we demonstrate the feasibility and clinical utility of comprehensive, NGS‐based genetic profiling for routine workup of advanced NSCLC based on the first 3,000 patients analyzed in our department. Following automated extraction of DNA and RNA from formalin‐fixed, paraffin‐embedded tissue samples, parallel sequencing of DNA and RNA for detection of mutations and gene fusions, respectively, was performed using PCR‐based enrichment with an ion semiconductor sequencing platform. Overall, 807 patients (27%) were eligible for currently approved, EGFR‐/BRAF‐/ALK‐ and ROS1‐directed therapies, while 218 additional cases (7%) with MET, ERBB2 (HER2) and RET alterations could potentially benefit from experimental targeted compounds. In addition, routine capturing of comutations, e.g. TP53 (55%), KEAP1 (11%) and STK11 (11%), as well as the precise typing of fusion partners and involved exons in case of actionable translocations including ALK and ROS1, are prognostic and predictive tools currently gaining importance for further refinement of therapeutic and surveillance strategies. The reliability, low dropout rates (<5%), minimal tissue requirements, fast turnaround times (6 days on average) and lower costs of the diagnostic approach presented here compared to sequential single‐gene testing, highlight its practicability in order to support individualized decisions in routine patient care, enrollment in molecularly stratified clinical trials, as well as translational research.
What's new?
Next‐generation sequencing (NGS) is an attractive option in the molecular workup of non‐small cell lung cancer (NSCLC). However, large‐scale implementation for routine diagnostics is a non‐trivial task. Here, the authors present the largest cohort of advanced NSCLC tested for mutations and translocations by combined targeted RNA‐ and DNA‐sequencing in routine diagnostics to date. The integrated approach exceeds current international guidelines and illustrates the performance and clinical impact of one‐stop shop NGS profiling. Due to amplification‐based sequencing, dropout rates are minimal and turnaround times low. By facilitating better patient stratification, such an approach can improve oncologic management and boost translational research.
Tumor mutational burden (TMB) is a new biomarker for prediction of response to PD-(L)1 treatment. Comprehensive sequencing approaches (i.e., whole exome and whole genome sequencing) are ideally ...suited to measure TMB directly. However, as their applicability in routine diagnostics is currently limited by high costs, long turnaround times and poor availability of fresh tissue, targeted next-generation sequencing (NGS) of formalin-fixed and paraffin-embedded (FFPE) samples appears to be a more feasible and straight-forward approach for TMB approximation, which can be seamlessly integrated in already existing diagnostic workflows and pipelines. In this work, we provide an overview of the clinical implications of TMB testing and highlight key parameters including pre-analysis, analysis and post-analytical steps that influence and shape TMB approximation by panel sequencing. Collectively, the data will not only serve as a field guide and state of the art knowledge source for molecular pathologists who consider implementation of TMB measurement in their lab, but also enable clinicians in understanding the specific parameters influencing TMB test results and reporting.
Soft-tissue sarcomas (STS) are rare malignancies that account for 1% of adult cancers and comprise more than 50 entities. Current therapeutic options for advanced-stage STS are limited. Immune ...checkpoint inhibitors targeting the PD-1/PD-L1 signaling axis are being explored as new treatment modality in STS; however, the determinants of response to these agents are largely unknown. Using the sarcoma data set of The Cancer Genome Altas (TCGA) and an independent cohort of untreated high-grade STS, we analyzed DNA copy number status and mRNA expression of PD-L1 in a total of 335 STS cases. Copy number gains (CNG) were detected in 54 TCGA cases (21.1%), of which 21 (8.2%) harbored focal PD-L1 CNG and that were most prevalent in myxofibrosarcoma (35%) and undifferentiated pleomorphic sarcoma (34%). In the untreated high-grade STS cohort, we detected CNG in six cases (7.6%). Analysis of co-amplified genes identified a 5.6-Mb core region comprising 27 genes, including JAK2. Patients with PD-L1 CNG had higher PD-L1 expression compared with STS without CNG (fold change, 1.8; p = 0.02), an effect that was most pronounced in the setting of focal PD-L1 CNG (fold change, 3.0; p = 0.0027). STS with PD-L1 CNG showed a significantly higher mutational load compared with tumors with a diploid PD-L1 locus (median number of mutated genes; 58 vs. 40; p = 3.6E-06), and PD-L1 CNG were associated with inferior survival (HR = 1.82; p = 0.025). In contrast, T-cell infiltrates quantified by mRNA expression of CD3Z were associated with improved survival (HR = 0.88; p = 0.024) and consequently influenced the prognostic power of PD-L1 CNG, with low CD3Z levels conferring poor survival in cases with PD-L1 CNG (HR = 1.8; p = 0.049). These data demonstrate that PD-L1 GNG and elevated expression of PD-L1 occur in a substantial proportion of STS, have prognostic impact that is modulated by T-cell infiltrates, and thus warrant investigation as response predictors for immune checkpoint inhibition.
The genetic landscape of rare benign tumours and their malignant counterparts is still largely unexplored. While recent work showed that mutant HRAS is present in subsets of poromas and ...porocarcinomas, a more comprehensive genetic view on these rare adnexal neoplasms is lacking. Using high-coverage next generation sequencing, we investigated the mutational profile of 50 cancer-related genes in 12 cases (six poromas and six porocarcinomas). Non-synonymous mutations were found in two-thirds of both poromas and porocarcinomas. Hotspot HRAS mutations were identified in two poromas (p.G13R and p.Q61R) and one porocarcinoma (p.G13C). While in poromas only few cases showed single mutated genes, porocarcinomas showed greater genetic heterogeneity with up to six mutated genes per case. Recurrent TP53 mutations were found in all porocarcinomas that harboured mutated genes. Non-recurrent mutations in porocarcinomas were found in several additional tumour suppressors (RB1, APC, CDKN2A, and PTEN), and genes implicated in PI3K-AKT and MAPK signalling pathways (ABL1, PDGFRA, PIK3CA, HRAS, and RET). UV-associated mutations were found in TP53, APC, CDKN2A, PTEN, and RET. In conclusion, our study confirms and extends the spectrum of genetic lesions in poromas and porocarcinomas. While poromas exhibited only few mutations, which did not involve TP53, the majority of porocarcinomas harboured UV-mediated mutations in TP53 with some of these cases showing considerable genetic heterogeneity that may be clinically exploitable.
Aberrant DNA methylation is frequently found in human malignancies including acute myeloid leukemia (AML). While most studies focus on later disease stages, the onset of aberrant DNA methylation ...events and their dynamics during leukemic progression are largely unknown.
We screened genome-wide for aberrant CpG island methylation in three disease stages of a murine AML model that is driven by hypomorphic expression of the hematopoietic transcription factor PU.1. DNA methylation levels of selected genes were correlated with methylation levels of CD34+ cells and lineage negative, CD127-, c-Kit+, Sca-1+ cells; common myeloid progenitors; granulocyte-macrophage progenitors; and megakaryocyte-erythroid progenitors.
We identified 1,184 hypermethylated array probes covering 762 associated genes in the preleukemic stage. During disease progression, the number of hypermethylated genes increased to 5,465 in the late leukemic disease stage. Using publicly available data, we found a significant enrichment of PU.1 binding sites in the preleukemic hypermethylated genes, suggesting that shortage of PU.1 makes PU.1 binding sites in the DNA accessible for aberrant methylation. Many known AML associated genes such as RUNX1 and HIC1 were found among the preleukemic hypermethylated genes. Nine novel hypermethylated genes, FZD5, FZD8, PRDM16, ROBO3, CXCL14, BCOR, ITPKA, HES6 and TAL1, the latter four being potential PU.1 targets, were confirmed to be hypermethylated in human normal karyotype AML patients, underscoring the relevance of the mouse model for human AML.
Our study identified early aberrantly methylated genes as potential contributors to onset and progression of AML.
Haematopoietic stem cells (HSCs) are responsible for the lifelong production of blood cells. The accumulation of DNA damage in HSCs is a hallmark of ageing and is probably a major contributing factor ...in age-related tissue degeneration and malignant transformation. A number of accelerated ageing syndromes are associated with defective DNA repair and genomic instability, including the most common inherited bone marrow failure syndrome, Fanconi anaemia. However, the physiological source of DNA damage in HSCs from both normal and diseased individuals remains unclear. Here we show in mice that DNA damage is a direct consequence of inducing HSCs to exit their homeostatic quiescent state in response to conditions that model physiological stress, such as infection or chronic blood loss. Repeated activation of HSCs out of their dormant state provoked the attrition of normal HSCs and, in the case of mice with a non-functional Fanconi anaemia DNA repair pathway, led to a complete collapse of the haematopoietic system, which phenocopied the highly penetrant bone marrow failure seen in Fanconi anaemia patients. Our findings establish a novel link between physiological stress and DNA damage in normal HSCs and provide a mechanistic explanation for the universal accumulation of DNA damage in HSCs during ageing and the accelerated failure of the haematopoietic system in Fanconi anaemia patients.
Myelodysplastic syndromes (MDSs) are a heterogeneous group of myeloid neoplasms with defects in hematopoietic stem and progenitor cells (HSPCs) and possibly the HSPC niche. Here, we show that ...patient-derived mesenchymal stromal cells (MDS MSCs) display a disturbed differentiation program and are essential for the propagation of MDS-initiating Lin−CD34+CD38− stem cells in orthotopic xenografts. Overproduction of niche factors such as CDH2 (N-Cadherin), IGFBP2, VEGFA, and LIF is associated with the ability of MDS MSCs to enhance MDS expansion. These factors represent putative therapeutic targets in order to disrupt critical hematopoietic-stromal interactions in MDS. Finally, healthy MSCs adopt MDS MSC-like molecular features when exposed to hematopoietic MDS cells, indicative of an instructive remodeling of the microenvironment. Therefore, this patient-derived xenograft model provides functional and molecular evidence that MDS is a complex disease that involves both the hematopoietic and stromal compartments. The resulting deregulated expression of niche factors may well also be a feature of other hematopoietic malignancies.
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•Disease-initiating cells in lower-risk MDS are restricted to Lin−CD34+CD38− subset•Myelodysplastic cells in patients reprogram mesenchymal stromal cells•Reprogrammed MSCs are essential for propagation of myelodysplastic syndromes•MDS and niche cells interact via bidirectional signaling crosstalk
Myelodysplastic syndrome (MDS) stem and progenitor cells induce mesenchymal niche cells to adopt an altered expression pattern, which in turn supports MDS stem cell propagation in vivo.
In this study, we present integrated quantitative proteome, transcriptome, and methylome analyses of hematopoietic stem cells (HSCs) and four multipotent progenitor (MPP) populations. From the ...characterization of more than 6,000 proteins, 27,000 transcripts, and 15,000 differentially methylated regions (DMRs), we identified coordinated changes associated with early differentiation steps. DMRs show continuous gain or loss of methylation during differentiation, and the overall change in DNA methylation correlates inversely with gene expression at key loci. Our data reveal the differential expression landscape of 493 transcription factors and 682 lncRNAs and highlight specific expression clusters operating in HSCs. We also found an unexpectedly dynamic pattern of transcript isoform regulation, suggesting a critical regulatory role during HSC differentiation, and a cell cycle/DNA repair signature associated with multipotency in MPP2 cells. This study provides a comprehensive genome-wide resource for the functional exploration of molecular, cellular, and epigenetic regulation at the top of the hematopoietic hierarchy.
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•Analysis identifies 6,000 proteins, 27,000 transcripts, and 15,000 DMRs in HSCs/MPPs•Core signaling, regulatory networks, and lncRNAs are central nodes in HSCs•Differentiation-associated changes include shifts in alternative transcript isoforms•DNA methylation correlates inversely with gene expression in HSCs and their progeny
This study identifies regulatory networks of primary mouse HSCs and four downstream MPPs by combining proteome, transcriptome, and DNA methylome analyses with in vitro and in vivo functional assays.
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