Comprehensive analysis of chromothripsis in 2,658 human cancers using whole-genome sequencing

Chromothripsis is a mutational phenomenon characterized by massive, clustered genomic rearrangements that occurs in cancer and other diseases. Recent studies in selected cancer types have suggested that chromothripsis may be more common than initially inferred from low-resolution copy-number data. Here, as part of the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA), we analyze patterns of chromothripsis across 2,658 tumors from 38 cancer types using whole-genome sequencing data. We find that chromothripsis events are pervasive across cancers, with a frequency of more than 50% in several cancer types. Whereas canonical chromothripsis profiles display oscillations between two copy-number states, a considerable fraction of events involve multiple chromosomes and additional structural alterations. In addition to non-homologous end joining, we detect signatures of replication-associated processes and templated insertions. Chromothripsis contributes to oncogene amplification and to inactivation of genes such as mismatch-repair-related genes. These findings show that chromothripsis is a major process that drives genome evolution in human cancer.

Abstract SY26-02: Sherlock-Lung: Tracing lung cancer mutational processes in never smokers

Globally, about 2 million people are diagnosed with lung cancer annually, making it the most common type of cancer in the world. In addition, lung cancer is the leading cause of cancer death among both men and women, accounting for ~25% of all cancer deaths in the United States and ~19% of cancer deaths worldwide. Although tobacco smoking is the most common cause of lung cancer, it is estimated that 10-25% of all patients diagnosed with lung cancer worldwide are never smokers, with higher proportions in Asians and women. Compared to former and current smokers with lung cancer, lung cancers in never smokers tend to present at an earlier age and more frequently have adenocarcinoma histology. Although a few risk factors are known to contribute to the etiology of lung cancer in never smokers, a large fraction of cancer cases cannot be explained by established environmental and genetic risk factors, highlighting the need for research in this area. One promising approach to identify the etiological factors involved in lung tumorigenesis in never smokers is based on the study of the “mutational signatures” that the exogenous and endogenous processes leave on the tumor tissue and surrounding areas. Somatic mutations accumulate throughout individuals’ lifetime, as a result of the balance between DNA damage and DNA repair. Mutational sources can change over time and mutational signatures can provide information on the tumor evolutionary trajectory, tracking activities of mutational processes. We designed “Sherlock-Lung” to identify mutational signatures in lung cancers from never smokers and order them based on their clonal and subclonal localization to have an insight on the factors involved in the initiation of the tumors. Prevention and treatment strategies are likely to be more effective when targeting the tumor initiating factors rather than those responsible for the tumor progression. Here, we present the Sherlock-Lung study design, which includes a combination of lung cancer cases from populations highly exposed to lung cancer risk factors and populations with unknown exposures. We also present preliminary data from this study and what we have learned from whole genome sequencing analysis of the mutational landscape of lung cancers from smokers and nonsmokers and from different histological subtypes. For example, although the mutational signature associated with tobacco smoking is largely clonal in all lung cancers from smokers, consistent with an initiating role of tobacco smoking in lung tumorigenesis, the mutational signatures distribution varies across histological subtypes. Moreover, the frequency of mutations in major cancer driver genes varies dramatically between smokers and never smokers, and mutational signatures distribution appears to differ between tumors with and without specific driver genes. In never smokers, without the dominant mutational source of tobacco smoking, other signatures emerged, e.g., that associated with reactive oxygen species. Although this approach has already revealed important information on the etiological processes involved in tumorigenesis of lung cancer and other cancer types, there is a growing list of open questions and challenges that need to be addressed. In population studies, careful exposure assessment to identify and validate new mutational signatures and the inclusion of study subjects from different geographical locations and ethnicities are critical.

Citation Format: Maria Teresa Landi, Tongwu Zhang, Montserrat Garcia-Closas, Yohan Bossé, Jianxin Shi, Bin Zhu, Qing Lan, Nathaniel Rothman, Jiyeon Choi, Neil E. Caporaso, Wei Zhao, Chongyi Chen, Eytan Ruppin, Jennifer Rosenbaum, Dmitry Gordenin, Sai Yendamuri, Chris Amos, Paul Brennan, David C. Christiani, Geoff Liu, Bonnie Gould Rothberg, Matthew Schabath, Han Liang, Ludmil Alexandrov, David Wedge, Stephen Chanock. Sherlock-Lung: Tracing lung cancer mutational processes in never smokers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr SY26-02.

Molecular Evolution of Early-Onset Prostate Cancer Identifies Molecular Risk Markers and Clinical Trajectories

Identifying the earliest somatic changes in prostate cancer can give important insights into tumor evolution and aids in stratifying high- from low-risk disease. We integrated whole genome, transcriptome and methylome analysis of early-onset prostate cancers (diagnosis ≤55 years). Characterization across 292 prostate cancer genomes revealed age-related genomic alterations and a clock-like enzymatic-driven mutational process contributing to the earliest mutations in prostate cancer patients. Our integrative analysis identified four molecular subgroups, including a particularly aggressive subgroup with recurrent duplications associated with increased expression of ESRP1, which we validate in 12,000 tissue microarray tumors. Finally, we combined the patterns of molecular co-occurrence and risk-based subgroup information to deconvolve the molecular and clinical trajectories of prostate cancer from single patient samples.

Abstract LB-378: Comprehensive analysis of chromothripsis in 2,658 human cancers using whole-genome sequencing

Chromothripsis is a newly discovered mutational phenomenon involving massive, clustered genomic rearrangements that occurs in cancer and other diseases. Recent studies in cancer suggest that chromothripsis may be far more common than initially inferred from low resolution DNA copy number data. Here, we analyze the patterns of chromothripsis across 2,658 tumors spanning 39 cancer types using whole-genome sequencing data. We find that chromothripsis events are pervasive across cancers, with a frequency of >50% in several cancer types. Whereas canonical chromothripsis profiles display oscillations between two copy number states, a considerable fraction of the events involves multiple chromosomes as well as additional structural alterations. In addition to non-homologous end-joining, we detect signatures of replicative processes and templated insertions. Chromothripsis contributes to oncogene amplification as well as to inactivation of genes such as mismatch-repair related genes. These findings show that chromothripsis is a major process driving genome evolution in human cancer.

Citation Format: Isidro Cortés-Ciriano, June-Koo Lee, Ruibin Xi, Dhawal Jain, Youngsook L. Jung, Lixing Yang, Dmitry Gordenin, Leszek J. Klimczak, Cheng-Zhong Zhang, David S. Pellman, Peter J. Park. Comprehensive analysis of chromothripsis in 2,658 human cancers using whole-genome sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-378.

Comprehensive molecular characterization and analysis of muscle-invasive urothelial carcinomas

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Background: We reported the integrated molecular analysis of 131 tumors in 2014 (Nature 507:315, 2014) and now report on the entire cohort of 412 tumors from the TCGA project in chemotherapy-naïve, muscle-invasive urothelial bladder cancer. Methods: Following strict clinical and pathologic quality control, tumors were analyzed for DNA copy number variants, somatic mutations (WES), DNA methylation, mRNA, non-coding RNA (lncRNA and miRNA) and (phospho-) protein expression, gene fusions, viral integration, pathway perturbation, clinical correlates, outcomes, and histopathology. Results: There was a high overall somatic mutation rate (8.2/Mb), as previously reported. There were 58 significantly mutated genes (SMGs) (MutSig_2CV), increased from 32 in the original report. We identified 5 mutation signatures including APOBEC-a and b, ERCC2, C > T_CpG, and a single ultra-mutated sample with a functional POLE mutation. APOBEC mutagenesis explained 70% of the mutation burden and was associated with survival (p = 0.0013). High mutation burden and neoantigen load were also associated with improved outcome (p = 0.00014 and 0.00078). The previously identified four mRNA subtypes were predicted on the larger set and also identified a novel poor-survival ‘neuronal’ subtype that nevertheless lacked small cell or neuroendocrine histology. Clustering converged for mRNA, lncRNA and miRNA expression, and for inferred activity of gene sets associated with regulator expression. We identified subsets with differential epithelial-mesenchymal transition scores, carcinoma-in-situ scores, and survival, with implications for distinct therapeutic potential. Conclusions: This integrated analysis of 412 TCGA patient samples validates and extends observations from the first 131 patients and significantly increases our power to detect additional low-frequency aberrations. The results provide unique insights into mechanisms of bladder cancer development, and identify novel subsets of MIBC that may benefit from differential treatment approaches.

Abstract 128: Comprehensive molecular characterization of 412 muscle-invasive urothelial bladder carcinomas: final analysis of The Cancer Genome Atlas (TCGA) project

Introduction: In 2014, TCGA's Bladder Cancer Working Group presented a preliminary integrated molecular analysis of 131 muscle-invasive urothelial carcinomas (Nature 507:315, 2014). We now report on the entire cohort of 412 fresh-frozen, chemotherapy-naïve tumors. Included in the analysis were paired blood and/or tumor-adjacent tissue samples. This is the largest sequencing project on bladder cancer to date. After strict clinical and pathologic quality control, tumors were analyzed for DNA copy number variants, somatic mutations, DNA methylation, mRNA, microRNA and (phospho-) protein expression, transcript splicing, gene fusions, viral integration, APOBEC mutagenesis, pathway perturbation, clinical correlates, and histopathology.

Results: There was a high overall somatic mutation rate (8.0/Mb), with a median of 245 and mean of 348 coding-region mutations per sample. That is the third highest mutation rate among the cancer types profiled by TCGA (after cutaneous melanoma and non-small cell lung cancers). We identified 54 genes as significantly mutated, compared with 32 in the original report on 131 tumors. TP53 mutations were the most common (49%), and also quite common were mutations in a number of chromatin-modifying genes, including MLL2 (29%), KDM6A (26%), ARID1A (25%), MLL3 (19%), EP300 (15%), CREBBP (12%), and MLL (11%). Other cancer-related genes showing frequent mutations included PIK3CA (22%), RB1 (17%), FGFR3 (14%), STAG2 (14%), ATM (14%), ELF3 (12%), FAT1 (12%), SPTAN1 (12%), ERBB2 (12%), ERBB3 (11%), ASXL2 (10%), ERCC2 (9%), CDKN1A (9%), TSC1 (8%), CDKN2A (7%), RHOB (6%), NFE2L2 (6%), PARD3 (6%), FAM47C (5%), RBM10 (5%),HRAS (5%), KRAS (4%), and PTEN (3%). High mutation burden was associated with improved outcome (p = 0.0004). APOBEC mutagenesis explained 70% of the mutation burden and was associated with survival. Gene silencing by promoter hypermethylation was identified in 167 genes with at least 5% frequency in the cohort. The previously identified four mRNA expression subtypes were again found in the complete set of 412 tumors, and the proportions of samples in each subtype were similar to the previous proportions. Reverse-phase proteomic array analysis of 344 of the samples revealed clusters associated with diagnostic subtype, pathological stage, and grade but not with smoking history or non-muscle invasive status.

Conclusions: This integrated molecular analysis of 412 TCGA tumor samples largely validates and considerably extends observations from the initial cohort of 131 patients. The larger cohort significantly increased our power to detect lower-frequency aberrations that were not identified in the original cohort. The results provide a robust basis for further functional studies of bladder cancer biology and also provide additional incisive information for the identification of molecular targets for therapy.

Citation Format: John N. Weinstein, Seth P. Lerner, David J. Kwiatkowski, Gad Getz, Jaegil Kim, Hikmat A. Al-ahmadie, Andrew D. Cherniack, Guangwu Guo, Rehan Akbani, Katherine A. Hoadley, William Y. Kim, Gordon Robertson, Andrew J. Mungall, Toshinori Hinoue, Peter W. Laird, Jonathan E. Rosenberg, Joaquim Bellmunt, Dean F. Bajorin, Margaret B. Morgan, Chad J. Creighton, Dmitry Gordenin, Joshua M. Stuart, Xiaoping Su, Michael C. Ryan, Jeffrey S. Damrauer, Wei Zhang, Yuexin Liu, Yiling Lu, Nikolaus Schultz, Raju Kucherlapati, Gordon B. Mills, Donna E. Hansel, Brian D. Robinson, Bodgen A. Czerniak, Victor E. Reuter. Comprehensive molecular characterization of 412 muscle-invasive urothelial bladder carcinomas: final analysis of The Cancer Genome Atlas (TCGA) project. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 128.

Abstract 987: Comprehensive characterization of urothelial bladder cancer: a TCGA Project update

Urothelial carcinoma (UC) is a major cause of morbidity and mortality for which there are no approved molecularly targeted agents and few good treatment options beyond cisplatin-based chemotherapy. As part of The Cancer Genome Atlas (TCGA) Project, we analyzed 131 chemotherapy-naive, muscle-invasive UC tumors for somatic mutations, DNA copy number variants (CNVs), mRNA and microRNA expression, protein expression and phosphorylation, DNA methylation, transcript splicing, gene fusion, viral integration, pathway perturbation, clinical correlates, and histopathology (TCGA Research Network, Nature, in press). Whole-exome sequencing showed 29 recurrently mutated genes. Potential therapeutic targets include altered PIK3CA, ERBB2, FGFR3, TSC1, and ERBB3, plus mutated chromatin-regulating genes MLL, MLL2, MLL3, CREBBP, CHD7, SRCAP, ARID1A, KDM6A (UTX), and EP300. There were 22 arm-level CNVs and 27 focally amplified or deleted regions. CDKN2A was deleted in 47%. Low-pass whole genome sequencing identified FGFR3-TACC3 fusions. Viral DNA was identified in 6% (CMV, HHV6B, HPV16, BK polyoma), and viral transcripts were identified in 4% (CMV, BK polyoma, HPV16).

. mRNA-seq identified 4 tumor clusters. Cluster I shows papillary morphology and FGFR3 dysregulation. Clusters I and II express high HER2 (ERBB2) and estrogen receptor beta signaling signature, sharing features with Luminal A breast cancer. Cluster III shows similarities to Basal-like breast and squamous cell head and neck carcinomas.

. Integrated analyses confirm alteration of multiple pathways, including cell cycle regulation (93%), kinase and PI3-K signaling (72%), and epigenetic regulation (histone-modifiers: 89%; SWI/SNF nucleosome remodeling complex: 64%). Recurrent alterations in the PI3-kinase/AKT/mTOR pathway (42%) and RTK/RAS pathway (44%) are potentially actionable.

. Overall, this study and others have identified multiple druggable targets in UC. FGFR3 is activated by mutation, gene fusion, and overexpression, suggesting clinical trials of FGFR3 inhibitors. PI3-kinase/mTOR/AKT/TSC1 pathway alterations are frequent, and mutation in TSC1 has been associated with response to mTOR inhibitors. ERBB2 amplifications and activating mutations may be targetable with agents such as trastuzumab, trastuzumab-DM1, lapatinib, and neratinib. The frequent alterations in epigenetic regulatory pathways suggest trials of agents such as the bromodomain inhibitors. The project is now being updated on the basis of data on 117 additional tumors.

Citation Format: John N. Weinstein, Jaegil Kim, Chad J. Creighton, Rehan Akbani, Katherine A. Hoadley, William Y. Kim, Margaret B. Morgan, Toshinori Hinoue, Andrew Cherniack, Xiaoping Su, Andrew J. Mungall, Michael C. Ryan, Jonathan E. Rosenberg, Dean F. Bajorin, Bogdan Czerniak, Donna Hansel, Victor E. Reuter, Brian D. Robinson, Hikmat A. Al-Ahmadie, Jeffrey S. Damrauer, Wei Zhang, Yuexin Liu, Dmitry Gordenin, Joshua M. Stuart, Nikolaus Schultz, Gordon Robertson, Raju Kucherlapati, Peter W. Laird, Gordon B. Mills, David J. Kwiatkowski, Seth P. Lerner, representing TCGA's Bladder Cancer Working Group. Comprehensive characterization of urothelial bladder cancer: a TCGA Project update. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 987. doi:10.1158/1538-7445.AM2014-987

Biased distribution of inverted and direct Alus in the human genome: implications for insertion, exclusion, and genome stability

Alu sequences, the most abundant class of large dispersed DNA repeats in human chromosomes, contribute to human genome dynamics. Recently we reported that long inverted repeats, including human Alus, can be strong initiators of genetic change in yeast. We proposed that the potential for interactions between adjacent, closely related Alus would influence their stability and this would be reflected in their distribution. We have undertaken an extensive computational analysis of all Alus (the database is at http://dir.niehs.nih.gov/ALU) to better understand their distribution and circumstances under which Alu sequences might affect genome stability. Alus separated by <650 bp were categorized according to orientation, length of regions sharing high sequence identity, distance between highly identical regions, and extent of sequence identity. Nearly 50% of all Alu pairs have long alignable regions (>275 bp), corresponding to nearly full-length Alus, regardless of orientation. There are dramatic differences in the distributions and character of Alu pairs with closely spaced, nearly identical regions. For Alu pairs that are directly repetitive, approximately 30% have highly identical regions separated by <20 bp, but only when the alignments correspond to near full-size or half-size Alus. The opposite is found for the distribution of inverted repeats: Alu pairs with aligned regions separated by <20 bp are rare. Furthermore, closely spaced direct and inverted Alus differ in their truncation patterns, suggesting differences in the mechanisms of insertion. At larger distances, the direct and inverted Alu pairs have similar distributions. We propose that sequence identity, orientation, and distance are important factors determining insertion of adjacent Alus, the frequency and spectrum of Alu-associated changes in the genome, and the contribution of Alu pairs to genome instability. Based on results in model systems and the present analysis, closely spaced inverted Alu pairs with long regions of alignment are likely at-risk motifs (ARMs) for genome instability.

Altered replication and inverted repeats induce mismatch repair-independent recombination between highly diverged DNAs in yeast

Replication, DNA organization, and mismatch repair (MMR) can influence recombination. We examined the effects of altered replication due to a mutation in the polymerase delta gene, long inverted repeats (LIRs) in motifs similar to those in higher eukaryotes, and MMR on intrachromosomal recombination between highly diverged (28%) truncated genes in Saccharomyces cerevisiae. A combination of altered replication and an LIR increased recombination up to 700-fold, while each alone led to a 3- to 20-fold increase. Homeologous recombination was not altered by pms1, msh2, and msh3 mismatch repair mutations. Similar to our previous observations for replication slippage-mediated deletions, there were > or = 5-bp identical runs at the recombination breakpoints. We propose that the dramatic increase in recombination results from enhancement of the effects of altered replication by the LIR, leading to recombinationally active initiating structures. Such interactions predict replication-related, MMR-independent genome changes.