Whole-Genome Sequencing Reveals Mutational Signatures Related to Radiation-Induced Sarcomas and DNA-Damage-Repair Pathways.

Radiation-induced sarcoma (RIS) is a rare but serious late complication arising from radiotherapy. Despite unfavorable clinical outcomes, the genomic footprints of ionizing radiation in RIS development remain largely unknown. Hence, this study aimed to characterize RIS genomes and the genomic alterations in them. We analyzed whole-genome sequencing in 11 RIS genomes matched with normal genomes to identify somatic alterations potentially associated with RIS development. Furthermore, the abundance of mutations, mutation signatures, and structural variants in RIS were compared with those in radiation-naïve spontaneous sarcomas. The mutation abundance in RIS genomes, including one hypermutated genome, was variable. Cancer-related genes might show different types of genomic alterations. For instance, NF1, NF2, NOTCH1, NOTCH2, PIK3CA, RB1, and TP53 showed singleton somatic mutations; MYC, CDKN2A, RB1, and NF1 showed recurrent copy number alterations; and NF2, ARID1B, and RAD51B showed recurrent structural variations. The genomic footprints of nonhomologous end joining are prevalent at indels of RIS genomes compared with those in spontaneous sarcoma genomes, representing the genomic hallmark of RIS genomes. In addition, frequent chromothripsis was identified along with predisposing germline variants in the DNA-damage-repair pathways in RIS genomes. The characterization of RIS genomes on a whole-genome sequencing scale highlighted that the nonhomologous end joining pathway was associated with tumorigenesis, and it might pave the way for the development of advanced diagnostic and therapeutic strategies for RIS.

Phase 2 study of afatinib among patients with recurrent and/or metastatic esophageal squamous cell carcinoma.

BACKGROUND: The objective of the current study was to investigate the clinical activity of, safety of, and predictive biomarkers for afatinib, an irreversible pan-ErbB kinase inhibitor, in patients with recurrent and/or metastatic esophageal squamous cell carcinoma (R/M-ESCC). METHODS: Patients with R/M-ESCC that was refractory to platinum-based chemotherapy were enrolled in the current multicenter, single-arm, phase 2 study and received afatinib at a dose of 40 mg/day. The primary endpoint was the objective response rate. Secondary endpoints included progression-free survival, overall survival, the disease control rate, and the safety profile. To identify predictive biomarkers, single-nucleotide variations, short insertions/deletions, and somatic copy number alterations were assessed using whole-exome sequencing and their associations with clinical outcomes were analyzed. RESULTS: Among 49 enrolled patients, the objective response rate and disease control rate were 14.3% and 73.3%, respectively. With a median follow-up of 6.6 months, the median progression-free survival and overall survival were 3.4 months and 6.3 months, respectively. Treatment-related adverse events were noted to have occurred in 33 patients (67.3%), with the majority being of grade 1 to 2 (adverse events were graded and recorded based on the National Cancer Institute Common Terminology Criteria for Adverse Events [version 4.03]). Whole-exome sequencing demonstrated that the ESCC genomes of patients who demonstrated a response to afatinib were enriched with genomic alterations of TP53 and epidermal growth factor receptor (EGFR). As a predictive marker, a score derived from TP53 disruptive mutations and EGFR amplifications and/or missense mutations demonstrated a significant association with the response to afatinib. The score based on the mutational status of EGFR and TP53 achieved a performance of an area under the curve of 0.86 in predicting the sensitivity of afatinib. CONCLUSIONS: The results of the current study demonstrated that afatinib can confer modest clinical benefits with manageable toxicity in patients with platinum-resistant R/M-ESCC. Identification of TP53 alterations and EGFR amplifications may serve as predictive markers with which to identify patients with R/M-ESCC who may benefit from afatinib. LAY SUMMARY: Esophageal squamous cell carcinoma (ESCC) is a type of cancer with a dismal prognosis and very limited treatment options. The clinical efficacy of afatinib was evaluated in patients with recurrent and/or metastatic ESCC, with adverse events demonstrating the modest efficacy with manageable toxicity of this irreversible, pan-ErbB kinase inhibitor. Whole-exome sequencing analysis of 41 cases of ESCC further revealed that the patients harboring epidermal growth factor receptor (EGFR) amplifications and disruptive TP53 mutations are more likely to benefit from treatment with afatinib. The results of the current study have highlighted the clinical value of EGFR and TP53 as predictive biomarkers of platinum-resistant recurrent and/or metastatic ESCC for afatinib sensitivity.

Mouse-human co-clinical trials demonstrate superior anti-tumour effects of buparlisib (BKM120) and cetuximab combination in squamous cell carcinoma of head and neck.

BACKGROUND: Recurrent and/or metastatic squamous cell carcinoma of head and neck (R/M SCCHN) is a common cancer with high recurrence and mortality. Current treatments have low response rates (RRs). METHODS: Fifty-three patients with R/M SCCHN received continuous oral buparlisib. In parallel, patient-derived xenografts (PDXs) were established in mice to evaluate resistance mechanisms and efficacy of buparlisib/cetuximab combination. Baseline and on-treatment tumour genomes and transcriptomes were sequenced. Based on the integrated clinical and PDX data, 11 patients with progression under buparlisib monotherapy were treated with a combination of buparlisib and cetuximab. RESULTS: For buparlisib monotherapy, disease control rate (DCR) was 49%, RR was 3% and median progression-free survival (PFS) and overall survival (OS) were 63 and 143 days, respectively. For combination therapy, DCR was 91%, RR was 18% and median PFS and OS were 111 and 206 days, respectively. Four PDX models were originated from patients enrolled in the current clinical trial. While buparlisib alone did not inhibit tumour growth, combination therapy achieved tumour inhibition in three of seven PDXs. Genes associated with apoptosis and cell-cycle arrest were expressed at higher levels with combination treatment than with buparlisib or cetuximab alone. CONCLUSIONS: The buparlisib/cetuximab combination has significant promise as a treatment strategy for R/M SCCHN. CLINICAL TRIAL REGISTRATION: NCT01527877.

Distinct mutation profiles between primary bladder cancer and circulating tumor cells warrant the use of circulating tumors cells as cellular resource for mutation follow-up.

BACKGROUND: While circulating tumor cells may serve as minimally invasive cancer markers for bladder cancers, the relationship between primary bladder cancers and circulating tumor cells in terms of somatic mutations is largely unknown. Genome sequencing of bladder tumor and circulating tumor cells is highlighted to identify the somatic mutations of primary bladder cancer. METHODS: Bladder cancer tissue was collected by transurethral resection of the bladder and preserved by snap-freezing. Circulating tumor cells were Isolated from the blood obtained before treatment. We performed whole exome sequencing of 20 matched pairs of primary bladder cancers and circulating tumor cells to identify and compare somatic mutations of these two different genomic resources. RESULTS: We observed that mutation abundances of primary bladder cancers and circulating tumor cells were highly variable. The mutation abundance was not significantly correlated between matched pairs. Of note, the mutation concordance between two resources was only 3-24% across 20 pairs examined, suggesting that the circulating tumor cell genomes of bladder cancer patients might be genetically distinct from primary bladder cancers. A relative enrichment of mutations belonging to APOBEC-related signature and a depletion of C-to-G transversions were observed for primary- and circulating tumor cells specific mutations, respectively, suggesting that distinct mutation forces might have been operative in respective lesions during carcinogenesis. CONCLUSIONS: The observed discrepancy of mutation abundance and low concordance level of mutations between genomes of primary bladder cancers and circulating tumor cells should be taken into account when evaluating clinical utility of circulating tumor cells for treatments and follow-up of bladder cancers. TRIAL REGISTRATION: Patients were selected and registered retrospectively, and medical records were evaluated.

Mutation heterogeneity between primary gastric cancers and their matched lymph node metastases.

BACKGROUND: The acquisition of an invasive phenotype by a tumor cell is a crucial step of malignant transformation. The underlying genetic mechanisms in gastric cancer (GC) are not well understood. METHODS: We performed whole-exome sequencing of 15 pairs of primary GC and their matched lymph node (LN) metastases (10 primary GCs with single matched LNs and 5 primary GCs with three LNs per case, respectively). Somatic alterations including single nucleotide variations, short insertions/deletions including locus-level microsatellite instability and copy number alterations were identified and compared between the primary and metastatic LN genomes. RESULTS: Mutation abundance was comparable between the primary GC and LN metastases, but the extent of mutation overlap or the mutation heterogeneity between primary and LN genomes varied substantially. Primary- or LN-specific mutations could be distinguished from common mutations in terms of mutation spectra and functional categories, suggesting that the mutation forces are not constant during gastric carcinogenesis. A spatial distribution revealed TP53 mutations as common mutations along with a number of region-specific mutations, such as primary-specific SMARCA4 and LN-specific CTNNB1 mutations. The subclonal architectures of common mutations were largely conserved between primary GC and LN metastatic genomes. The mutation-based phylogenetic analyses further showed that LN metastases may have arisen from homogeneous subclones of primary tumors. CONCLUSIONS: The abundance and spatial distribution of mutations may provide clues on the evolutionary relationship between primary and matched LN genomes. Gene-level analyses further distinguished the early addicted cancer drivers such as TP53 mutations from late acquired region-specific mutations.

Fusobacterium nucleatum induces a tumor microenvironment with diminished adaptive immunity against colorectal cancers.

Background & Aims: Fusobacterium nucleatum (FN) plays a pivotal role in the development and progression of colorectal cancer by modulating antitumor immune responses. However, the impact of FN on immune regulation in the tumor microenvironment has not been fully elucidated. Methods: The abundance of FN was measured in 99 stage III CRC tumor tissues using quantitative polymerase chain reaction. Gene expression profiles were assessed and annotated using consensus molecular subtypes (CMS), Gene Ontology (GO) analysis, and deconvolution of individual immune cell types in the context of FN abundance. Immune profiling for tumor infiltrating T cells isolated from human tumor tissues was analyzed using flow cytometry. Ex vivo tumor-infiltrating T cells were stimulated in the presence or absence of FN to determine the direct effects of FN on immune cell phenotypes. Results: Gene expression profiles, CMS composition, abundance of immune cell subtypes, and survival outcomes differed depending on FN infection. We found that FN infection was associated with poorer disease-free survival and overall survival in stage III CRC patients. FN infection was associated with T cell depletion and enrichment of exhausted CD8+ and FoxP3+ regulatory T cells in the tumor microenvironment. The presence of FN in tumors was correlated with a suppressive tumor microenvironment in a T cell-dependent manner. Conclusion: FN enhanced the suppressive immune microenvironment with high depletion of CD8+ T cells and enrichment of FoxP3+ regulatory T cells in human colorectal cancer cases. Our findings suggest a potential association for FN in adaptive immunity, with biological and prognostic implications.

Correlation-based and feature-driven mutation signature analyses to identify genetic features associated with DNA mutagenic processes in cancer genomes.

Mutation signatures represent unique sequence footprints of somatic mutations resulting from specific DNA mutagenic and repair processes. However, their causal associations and the potential utility for genome research remain largely unknown. In this study, we performed PanCancer-scale correlative analyses to identify the genomic features associated with tumor mutation burdens (TMB) and individual mutation signatures. We observed that TMB was correlated with tumor purity, ploidy, and the level of aneuploidy, as well as with the expression of cell proliferation-related genes representing genomic covariates in evaluating TMB. Correlative analyses of mutation signature levels with genes belonging to specific DNA damage-repair processes revealed that deficiencies of NHEJ1 and ALKBH3 may contribute to mutations in the settings of APOBEC cytidine deaminase activation and DNA mismatch repair deficiency, respectively. We further employed a strategy to identify feature-driven, de novo mutation signatures and demonstrated that mutation signatures can be reconstructed using known causal features. Using the strategy, we further identified tumor hypoxia-related mutation signatures similar to the APOBEC-related mutation signatures, suggesting that APOBEC activity mediates hypoxia-related mutational consequences in cancer genomes. Our study advances the mechanistic insights into the TMB and signature-based DNA mutagenic and repair processes in cancer genomes. We also propose that feature-driven mutation signature analysis can further extend the categories of cancer-relevant mutation signatures and their causal relationships.

Mutation Analysis of Colorectal and Gastric Carcinomas Originating from Adenomas: Insights into Genomic Evolution Associated with Malignant Progression.

Small malignant tumor foci arising from benign lesions are rare but offer a unique opportunity to investigate the genomic evolution that occurs during malignant transformation. In this study, we analyzed 11 colorectal and 10 gastric adenoma-carcinoma pairs, each of which represented malignant tumors (carcinomas) embedded in benign lesions (adenomas) found in the same patient. Whole-exome sequencing revealed that mutation abundance was variable across different cases, but comparable between adenoma-carcinoma pairs. When mutations were classified as adenoma-specific, carcinoma-specific, or common, adenoma-specific mutations were more enriched with subclonal mutations than were carcinoma-specific mutations, indicative of a perturbation in mutational subclonal architecture (such as selective sweep) during malignant transformation. Among the recurrent mutations in colorectal cancers, APC and KRAS mutations were common between adenomas and carcinomas, indicative of their early occurrence during genomic evolution. TP53 mutations were often observed as adenoma-specific and therefore likely not associated with the emergence of malignant clones. Clonality-based enrichment analysis revealed that subclonal mutations of extracellular matrix genes in adenomas are more likely to be clonal in carcinomas, indicating potential roles for these genes in malignant transformation. Compared with colorectal cancers, gastric cancers showed more lesion-specific mutations than common mutations and higher levels of discordance in copy number profiles between matched adenomas and carcinomas, which may explain the elevated evolutionary dynamics and heterogeneity of gastric cancers compared to colorectal cancers. Taken together, this study demonstrates that co-existing benign and malignant lesions enable the evolution-based categorization of genomic alterations that may reveal clinically important biomarkers in colorectal and gastric cancers.

Genomic, transcriptomic, and viral integration profiles associated with recurrent/metastatic progression in high-risk human papillomavirus cervical carcinomas.

Acquisition of recurrent/metastatic potential by a tumor cell defines a critical step in malignant progression. However, understanding of metastatic progression at the molecular level is scarce for cervical carcinomas (CES). In this study, we performed genomic, transcriptomic, and viral profiling of five pairs of primary (CES-P) and matched recurrent/metastatic tumors (CES-R/M) with high risk human papillomavirus. Whole exome sequencing revealed mutation features of CES-R/M including elevated mutation burdens and prevalent copy number alterations compared to their matched CES-P. A relative deficit of APOBEC-related mutation signatures accompanying the transcriptional downregulation of APOBEC3A was observed for CES-R/M. Mutations in genes encoding epigenetic regulators were commonly observed as CES-R/M-specific alterations. Immunoprofiling and gene set analysis revealed CES-Ps were enriched with transcripts representing activated anticancer immunity such as interferon-gamma pathway, while CES-R/M exhibited upregulation of genes involved in epithelial-mesenchymal transition and angiogenesis. Viral capture sequencing revealed that integration sites remained enriched in viral E1 protein domain during malignant progression. Moreover, we found transcriptional upregulation of POSTN and downregulation of APOBEC3A were associated with unfavorable clinical outcomes in CES. Comprehensive genomic and transcriptomic profiling of a rare cohort including CES-R/M identified metastases-specific features to advance the molecular understanding into CES metastatic progression with potential clinical implications.

Identification of Local Clusters of Mutation Hotspots in Cancer-Related Genes and Their Biological Relevance.

Mutation hotspots are either solitary amino acid residues or stretches of amino acids that show elevated mutation frequency in cancer-related genes, but their prevalence and biological relevance are not completely understood. Here, we developed a Smith-Waterman algorithm-based mutation hotspot discovery method, MutClustSW, to identify mutation hotspots of either single or clustered amino acid residues. We identified 181 missense mutation hotspots from COSMIC and TCGA mutation databases. In addition to 77 single amino acid residue hotspots (42.5 percent) including well-known mutation hotspots such as IDH1 (p.R132) and BRAF (p.V600), we identified 104 mutation hotspots (57.5 percent) as clusters or stretches of multiple amino acids, and the hotspots on MUC2, EPPK1, KMT2C, and TP53 were larger than 50 amino acids. Twelve of 27 nonsense mutation hotspots (44.4 percent) were observed in four cancer-related genes, TP53, ARID1A, CDKN2A, and PTEN, suggesting that truncating mutations on some tumor suppressor genes are not randomly distributed as previously assumed. We also show that hotspot mutations have higher mutation allele frequency than non-hotspots, and the hotspot information can be used to prioritize the cancer drivers. Together, the proposed algorithm and the mutation hotspot information can serve as valuable resources in the selection of functional driver mutations and associated genes.

Impact of Tumor Purity on Immune Gene Expression and Clustering Analyses across Multiple Cancer Types.

Surgical archives of tumor specimens are often impure. The presence of RNA transcripts from nontumor cells, such as immune and stromal cells, can impede analyses of cancer expression profiles. To systematically analyze the impact of tumor purity, the gene expression profiles and tumor purities were obtained for 7,794 tumor specimens across 21 tumor types (available in The Cancer Genome Atlas consortium). First, we observed that genes with roles in immunity and oxidative phosphorylation were significantly inversely correlated and correlated with the tumor purity, respectively. The expression of genes implicated in immunotherapy and specific immune cell genes, along with the abundance of immune cell infiltrates, was substantially inversely correlated with tumor purity. This relationship may explain the correlation between immune gene expression and mutation burden, highlighting the need to account for tumor purity in the evaluation of expression markers obtained from bulk tumor transcriptome data. Second, examination of cluster membership of gene pairs, with or without controlling for tumor purity, revealed that tumor purity may have a substantial impact on gene clustering across tumor types. Third, feature genes for molecular taxonomy were analyzed for correlation with tumor purity, and for some tumor types, feature genes representing the mesenchymal and classical subtypes were inversely correlated and correlated with tumor purity, respectively. Our findings indicate that tumor purity is an important confounder in evaluating the correlation between gene expression and clinicopathologic features such as mutation burden, as well as gene clustering and molecular taxonomy. Cancer Immunol Res; 6(1); 87-97. ©2017 AACR.