Existing methods to improve detection of circulating tumor DNA (ctDNA) have focused on sensitivity for detecting genomic alterations but have rarely considered the biological properties of plasma cell-free DNA (cfDNA). We hypothesized that differences in fragment lengths of circulating DNA could be exploited to enhance sensitivity for detecting the presence of ctDNA and for non-invasive genomic analysis of cancer. We surveyed ctDNA fragment sizes in 344 plasma samples from 200 cancer patients using low-pass whole-genome sequencing (0.4×). To establish the size distribution of mutant ctDNA, tumor-guided personalized deep sequencing was performed in 19 patients. We detected enrichment of ctDNA in fragment sizes between 90–150 bp, and developed methods for in vitro and in silico size selection of these fragments. Selecting fragments between 90–150 bp improved detection of tumor DNA, with more than 2-fold median enrichment in >95% of cases, and more than 4-fold enrichment in >10% of cases. Analysis of size-selected cfDNA identified clinically actionable mutations and copy number alterations that were otherwise not detected. Identification of plasma samples from patients with advanced cancer was improved by predictive models integrating fragment length and copy number analysis of cfDNA, with AUC>0.99 compared to AUC<0.80 without fragmentation features. Increased identification of cfDNA from patients with glioma, renal, and pancreatic cancer was achieved with AUC>0.91, compared to AUC<0.5 without fragmentation features. Fragment size analysis and selective sequencing of specific fragment sizes can boost ctDNA detection and could complement or provide an alternative to deeper sequencing of cell-free DNA for clinical applications, earlier diagnosis and study of tumor biology.

The genomic complexity of profound copy number aberrations has prevented effective molecular stratification of ovarian cancers. Here, to decode this complexity, we derived copy number signatures from shallow whole-genome sequencing of 117 high-grade serous ovarian cancer (HGSOC) cases, which were validated on 527 independent cases. We show that HGSOC comprises a continuum of genomes shaped by multiple mutational processes that result in known patterns of genomic aberration. Copy number signature exposures at diagnosis predict both overall survival and the probability of platinum-resistant relapse. Measurement of signature exposures provides a rational framework to choose combination treatments that target multiple mutational processes.

Genomic complexity from profound copynumber aberration has prevented effective molecular stratification of ovarian and other cancers. Here we present a method for copynumber signature identification that decodes this complexity. We derived eight signatures using 117 shallow wholegenome sequenced highgrade serous ovarian cancer cases, which were validated on a further 497 cases. Mutational processes underlying the copynumber signatures were identified, including breakagefusionbridge cycles, homologous recombination deficiency and wholegenome duplication. We show that most tumours are heterogeneous and harbour multiple signature exposures. We also demonstrate that copy number signatures predict overall survival and changes in signature exposure observed in response to chemotherapy suggest potential treatment strategies. 2. CC-BY-NC-ND 4.0 International license not peer-reviewed) is the author/funder. It is made available under aThe copyright holder for this preprint (which was . http://dx.doi.org/10.1101/174201 doi: bioRxiv preprint first posted online Aug. 9, 2017;The discrete mutational processes that drive copynumber change in human cancers are not readily identifiable from genomewide sequence data. This presents a major challenge for the development of precision medicine for cancers that are strongly dominated by copynumber changes, including highgrade serous ovarian (HGSOC), oesophageal, nonsmallcell lung and triple negative breast cancers 1 . These tumours have low frequency of recurrent oncogenic mutations, few recurrent copy number alterations and highly complex genomic profiles 2 .HGSOCs are poor prognosis carcinomas with ubiquitous TP53 mutation 3 . Despite efforts to discover new molecular subtypes and targeted therapies, overall survival has not improved over two decades 4 . Current genomic stratification is limited to defining homologous recombinationdeficient (HRD) tumours 57 , and classification using gene expression does not currently have clinical utility 8,9 . Detailed genomic analysis using whole genome sequencing has shown frequent loss of RB1, NF1 and PTEN by gene breakage events 10 and enrichment of amplification associated foldback inversions in nonHRD tumours 11 . However, none of these approaches has provided a broad mechanistic understanding of HGSOC, reflecting the challenges of detecting classifiers in extreme genomic complexity.Recent algorithmic advances have enabled interpretation of complex genomic changes by identifying mutational signatures genomic patterns that are the imprint of mutagenic processes accumulated over the lifetime of a cancer cell . Importantly, these studies show that tumours typically harbour multiple mutational processes requiring computational approaches that can robustly identify coexistent mutational signatures. Quantification of the exposure of a tumour to specific mutational signatures provides a rational framework to personalise therapy 14 but currently is not readily applicable to copynumber driven tumours. We hypothesized that specific feat...

The authors have no direct conflicts of interest to declare. B.Y. Karlan served on Invitae Corporation's Advisory Board from 2017 to 2018. I. McNeish has acted on Advisory Boards for AstraZeneca, Clovis Oncology, Tesaro, Carrick Therapeutics and Takeda. His institution receives funding from AstraZeneca. R. Glasspool is on the Advisory Boards for AstraZeneca, Tesaro, Clovis and Immunogen and does consultancy work for SOTIO. She has received support to attend conferences from AstraZeneca, Roche and Tesaro. Her institution has received research funding from Boehringer Ingelheim and Lilly/Ignyta and she is the national co-ordinating investigator for the UK for trials sponsored by AstraZeneca and Tesaro and site principal investigator for trials sponsored by AstraZeneca, Tesaro, Immunogen, Pfizer, Lilly and Clovis. P. Fasching has received grants from Novartis, Biontech and Cepheid as well as personal fees from

PURPOSE Germline BRCA1 and/or BRCA2 mutations (gBRCAms) are risk factors for pancreatic cancer. The extent to which demographic and geographic factors affect the uptake of gBRCAm testing in pancreatic cancer (PC) is unknown. METHODS We conducted a retrospective, descriptive analysis of demographic/geographic data from the first 2,206 patients with metastatic PC (mPC) screened for eligibility to enter the phase III POLO trial of maintenance olaparib. No formal statistical tests were performed. RESULTS Of 2,167 patients with previously unknown gBRCAm status, 128 (5.9%) had a newly identified gBRCAm; rates were highest in the United States, France, and Israel (9.5%, 7.6%, and 7.4%, respectively). When including patients with a previously known gBRCAm, prevalence rose to 7.2% (or 5.8% after excluding populations enriched in Ashkenazi Jews, who are known to have a high rate of BRCA1 and BRCA2 founder mutations). Patients with a gBRCAm were slightly younger (57.9 v 61.1 years) and more likely to have early-onset mPC than those without. Higher newly identified gBRCAm prevalence was observed among African American (n = 28) versus white (n = 1,808), Asian (n = 218), and other (n = 61) patients (10.7% v 6.1%, 5.0%, and 1.6%, respectively). Of 139 white patients with a gBRCAm, 110 were newly identified during screening; the majority of gBRCAms in African American, Asian, and Hispanic patients (n = 3, n = 11, and n = 5, respectively) were newly identified. CONCLUSION We identified substantial geographic and some racial variability in gBRCAm prevalence among patients with mPC, an important consideration given the increased use of familial screening and possible future use of targeted therapies in this setting. Although our study included small numbers of nonwhite patients, prior knowledge of their gBRCAm status was limited compared with their white counterparts, which suggests disparities in genetic testing uptake.

PurposeThe known epithelial ovarian cancer (EOC) susceptibility genes account for less than 50% of the heritable risk of ovarian cancer suggesting that other susceptibility genes exist. The aim of this study was to evaluate the contribution to ovarian cancer susceptibility of rare deleterious germline variants in a set of candidate genes.MethodsWe sequenced the coding region of 54 candidate genes in 6385 invasive EOC cases and 6115 controls of broad European ancestry. Genes with an increased frequency of putative deleterious variants in cases versus controls were further examined in an independent set of 14 135 EOC cases and 28 655 controls from the Ovarian Cancer Association Consortium and the UK Biobank. For each gene, we estimated the EOC risks and evaluated associations between germline variant status and clinical characteristics.ResultsThe ORs associated for high-grade serous ovarian cancer were 3.01 for PALB2 (95% CI 1.59 to 5.68; p=0.00068), 1.99 for POLK (95% CI 1.15 to 3.43; p=0.014) and 4.07 for SLX4 (95% CI 1.34 to 12.4; p=0.013). Deleterious mutations in FBXO10 were associated with a reduced risk of disease (OR 0.27, 95% CI 0.07 to 1.00, p=0.049). However, based on the Bayes false discovery probability, only the association for PALB2 in high-grade serous ovarian cancer is likely to represent a true positive.ConclusionsWe have found strong evidence that carriers of PALB2 deleterious mutations are at increased risk of high-grade serous ovarian cancer. Whether the magnitude of risk is sufficiently high to warrant the inclusion of PALB2 in cancer gene panels for ovarian cancer risk testing is unclear; much larger sample sizes will be needed to provide sufficiently precise estimates for clinical counselling.

Introductory paragraph:Non-invasive analysis of cancer genomes using cell-free circulating tumour DNA (ctDNA) is being widely implemented for clinical indications. The sensitivity for detecting the presence of ctDNA and genomic changes in ctDNA is limited by its low concentration compared to cell-free DNA of nontumour origin. We studied the feasibility for enrichment of ctDNA by size selection, in plasma samples collected before and during chemotherapy treatment in 13 patients with recurrent highgrade serous ovarian cancer. We evaluated the effects using targeted and whole genome sequencing. Selecting DNA fragments between 90-150 bp before analysis yielded enrichment of mutated DNA fraction of up to 11-fold. This allowed identification of adverse copy number alterations, including MYC amplification, otherwise not observed. Size selection allows detection of tumour alterations masked by non-tumour DNA in plasma and could help overcome sensitivity limitations of liquid biopsy for applications in early diagnosis, detection of minimal residual disease, and genomic profiling. Lab for help and constructive discussion, in particular

Purpose: The known EOC susceptibility genes account for less than 50% of the heritable risk of ovarian cancer suggesting other susceptibility genes exist. The aim of this study was to evaluate the contribution to ovarian cancer susceptibility of rare deleterious germline variants in a set of candidate genes. Methods: We sequenced the coding region of 54 candidate genes in 6385 invasive EOC cases and 6115 controls of broad European ancestry. Genes with an increased frequency of putative deleterious variants in cases verses controls were further examined in an independent set of 14,146 EOC cases and 28,661 controls from the ovarian cancer association consortium and the UK Biobank. For each gene, we estimated the EOC risks and evaluated associations between germline variant status and clinical characteristics. Results: The odds ratios (OR) associated for high-grade serous ovarian cancer were 3.01 for PALB2 (95% CI 1.59-5.68; P = 0.00068), 1.99 for POLK (95% CI 1.15-3.43; P = 0.014), and 4.07 for SLX4 (95% CI 1.34-12.4; P = 0.013). Deleterious mutations in FBXO10 were associated with a reduced risk of disease (OR 0.27, 95% CI 0.07-1.00, P=0.049). However, based on the Bayes false discovery probability, only the association for PALB2 in high-grade serous ovarian cancer is likely to represent a true positive. Conclusions: We have found strong evidence that carriers of PALB2 deleterious mutations are at increased risk of high-grade serous ovarian cancer. Whether the magnitude of risk is sufficiently high to warrant the inclusion of PALB2 in cancer gene panels for ovarian cancer risk testing is unclear; much larger sample sizes will be needed to provide sufficiently precise estimates for clinical counselling.