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Purpose Structural variants (SVs) may be an underestimated cause of hereditary cancer syndromes given the current limitations of short-read next-generation sequencing. Here we investigated the utility of long-read sequencing in resolving germline SVs in cancer susceptibility genes detected through short-read genome sequencing. Methods Known or suspected deleterious germline SVs were identified using Illumina genome sequencing across a cohort of 669 advanced cancer patients with paired tumor genome and transcriptome sequencing. Candidate SVs were subsequently assessed by Oxford Nanopore long-read sequencing. Results Nanopore sequencing confirmed eight simple pathogenic or likely pathogenic SVs, resolving three additional variants whose impact could not be fully elucidated through short-read sequencing. A recurrent sequencing artifact on chromosome 16p13 and one complex rearrangement on chromosome 5q35 were subsequently classified as likely benign, obviating the need for further clinical assessment. Variant configuration was further resolved in one case with a complex pathogenic rearrangement affecting TSC2. Conclusion Our findings demonstrate that long-read sequencing can improve the validation, resolution, and classification of germline SVs. This has important implications for return of results, cascade carrier testing, cancer screening, and prophylactic interventions.

Introduction Uninformative germline genetic testing presents a challenge to clinical management for patients suspected to have Lynch syndrome, a cancer predisposition syndrome caused by germline variants in the mismatch repair (MMR) genes or EPCAM. Methods Among a consecutive series of MMR-deficient Lynch syndrome spectrum cancers identified through immunohistochemistry-based tumor screening, we investigated the clinical utility of tumor sequencing for the molecular diagnosis and management of suspected Lynch syndrome families. MLH1-deficient colorectal cancers were prescreened for BRAF V600E before referral for genetic counseling. Microsatellite instability, MLH1 promoter hypermethylation, and somatic and germline genetic variants in the MMR genes were assessed according to an established clinical protocol. Results Eighty-four individuals with primarily colorectal (62%) and endometrial (31%) cancers received tumor-normal sequencing as part of routine clinical genetic assessment. Overall, 27% received a molecular diagnosis of Lynch syndrome. Most of the MLH1-deficient tumors were more likely of sporadic origin, mediated by MLH1 promoter hypermethylation in 54% and double somatic genetic alterations in MLH1 (17%). MSH2-deficient, MSH6-deficient, and/or PMS2-deficient tumors could be attributed to pathogenic germline variants in 37% and double somatic events in 28%. Notably, tumor sequencing could explain 49% of cases without causal germline variants, somatic MLH1 promoter hypermethylation, or somatic variants in BRAF. Discussion Our findings support the integration of tumor sequencing into current Lynch syndrome screening programs to improve clinical management for individuals whose germline testing is uninformative.

For 21 putative BRCA1 and BRCA2 splice site variants, the concordance between mRNA analysis and predictions by in silico programs was evaluated. Aberrant splicing was confirmed for 12 alterations. In silico prediction tools were helpful to determine for which variants cDNA analysis is warranted, however, predictions for variants in the Cartegni consensus region but outside the canonical sites, were less reliable. Learning algorithms like Adaboost and Random Forest outperformed the classical tools. Further validations are warranted prior to implementation of these novel tools in clinical settings. Additionally, we report here for the first time activated cryptic donor sites in the large exon 11 of BRCA2 by evaluating the effect at the cDNA level of a novel tandem duplication (5' breakpoint in intron 4; 3' breakpoint in exon 11) and of a variant disrupting the splice donor site of exon 11 (c.6841+1G > C). Additional sites were predicted, but not activated. These sites warrant further research to increase our knowledge on cis and trans acting factors involved in the conservation of correct transcription of this large exon. This may contribute to adequate design of ASOs (antisense oligonucleotides), an emerging therapy to render cancer cells sensitive to PARP inhibitor and platinum therapies.

1582 Background: Recent literature cites a germline mutation rate of 3.9-15.1% in patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) depending on breadth of genes tested, pre-selection of high-risk history and population substructure. True incidence of germline mutations in PDAC is unknown in unselected population. Methods: All patients (pts) diagnosed with PDAC in the province of British Columbia, Canada and referred to the Hereditary Cancer Program, were eligible to undergo 30 gene Color saliva kit testing under a research protocol, or clinical multigene testing if they met existing local criteria regardless of whether they signed on to the protocol. Any healthcare provider or patients themselves could refer. Results: 243 pts were referred between August 2016 and October 2018 but 25.1% (61) declined and 9.1% (22) died before testing. Of the 141 pts who consented to research protocol and completed germline testing, median age was 64 (46.1-81.0), 68.8% were European, 1.4% Ashkenazi Jewish heritage, 42% male, 61% non-smoker, 24.1% had personal history of a second cancer and 39% had metastatic disease. Baseline characteristics were similar between the PV positive and uninformative group. 20/25 PV were in known PDAC susceptibility genes with cascade screening implications (ATM (9), BRCA2 (4), BRCA2/ATM (1), CDKN2A (4), and MSH2 (2)). Excluding the 3 PV identified through carrier testing (1) and prior research identification (2), the rate of PV in unselected, unrelated PDAC cohort is 22/138 (15.9%). Utilizing previous NCCN criteria for BRCA1/BRCA2 testing or for familial pancreatic cancer did not appear to select for patients with higher risk of PV positive (12/65 (18.4%) PV positive rate versus 13/76 (17.1%) in those that didn’t meet criteria). Previous criteria would have missed 52% (13/25) PV in ATM (6), BRCA2/ATM (1), BRCA2 (2), MSH2 (2), NBN (1), CHEK2 (1). To date, a third of families with PV identified have accessed cascade testing in 38 relatives. Conclusions: Given the high incidence of 15.9% PV in hereditary cancer susceptibility genes, our data support recommendations for universal germline genetic testing of PDAC pts.

We report a case of early-onset pancreatic ductal adenocarcinoma in a patient harboring biallelic MUTYH germline mutations, whose tumor featured somatic mutational signatures consistent with defective MUTYH-mediated base excision repair and the associated driver KRAS transversion mutation p.Gly12Cys. Analysis of an additional 730 advanced cancer cases (N = 731) was undertaken to determine whether the mutational signatures were also present in tumors from germline MUTYH heterozygote carriers or if instead the signatures were only seen in those with biallelic loss of function. We identified two patients with breast cancer each carrying a pathogenic germline MUTYH variant with a somatic MUTYH copy loss leading to the germline variant being homozygous in the tumor and demonstrating the same somatic signatures. Our results suggest that monoallelic inactivation of MUTYH is not sufficient for C:G>A:T transversion signatures previously linked to MUTYH deficiency to arise (N = 9), but that biallelic complete loss of MUTYH function can cause such signatures to arise even in tumors not classically seen in MUTYH-associated polyposis (N = 3). Although defective MUTYH is not the only determinant of these signatures, MUTYH germline variants may be present in a subset of patients with tumors demonstrating elevated somatic signatures possibly suggestive of MUTYH deficiency (e.g., COSMIC Signature 18, SigProfiler SBS18/SBS36, SignatureAnalyzer SBS18/SBS36).

OBJECTIVE: To determine the prevalence of Lynch syndrome mutations in a Canadian hereditary cancer clinic population, and to determine the effectiveness of the program’s referral criteria and testing algorithm.METHODS: A retrospective chart review of all patients who were referred for and received genetic counselling at the BC Cancer Agency’s Hereditary Cancer Program for a family history of colon cancer from August 1, 2004, to September 1, 2006, was performed. Charts were reviewed for referral criteria met, cancer history, whether testing was offered and the outcome of testing.RESULTS: Lynch syndrome was confirmed or highly suspected in 14.3% of index test patients (eight of 56) by the identification of a deleterious mutation or variant likely to be deleterious in either of thehMLH1orhMSH2mismatch repair genes. In the program, the two most effective criteria were a personal diagnosis of two or more primary Lynch syndrome-related cancers (one diagnosed at younger than 50 years of age) or two first-degree relatives with a Lynch syndrome-related cancer (both diagnosed at younger than 50 years of age). The respective positive predictive values of these two criteria were calculated to be 66.7% (95% CI 40% to 93%) and 58.3% (95% CI 30.4% to 86.2%).CONCLUSIONS: The Hereditary Cancer Program developed and successfully implemented an approach that selected individuals at risk for Lynch syndrome with a significant pretest probability of mutation of 14.3%. Improved ascertainment of families with Lynch syndrome will require greater physician awareness of referral criteria, program advances in the testing algorithm and a population-based approach to screening incident colon cancers.

Biallelic pathogenic germline variants in the DNA repair glycosylase, MUTYH, cause MUTYH-associated polyposis, characterised by an increased susceptibility to colorectal adenomas and carcinomas secondary to defective base excision repair. We report a patient diagnosed with Stage IIB distal pancreatic ductal adenocarcinoma (PDAC) at the age of 45 years. Prior colonoscopy and gastroscopy noted three colonic tubular adenomas and a gastric fundic gland polyp. The patient was consented to whole genome and transcriptome sequencing of the PDAC and matched normal blood DNA through the British Columbia Personalized Onco-Genomics (POG) program. Analysis of germline and somatic variants including single nucleotide variants, copy number determination, loss of heterozygosity detection and mutational signatures was undertaken. Expression fold-changes were calculated against Illumina BodyMap pancreatic tissue averages and compared against The Cancer Genome Atlas PDAC cases. Germline analysis revealed biallelic mutations in the MUTYH gene. In light of this patient's personal and family history of adenomatous colon polyps, clinic-initiated panel testing of 14 cancer susceptibility genes, including MUTYH, via Illumina sequencing with reflex Sanger confirmation revealed the same biallelic MUTYH changes. Analysis of the patient's PDAC revealed a base excision repair pathway signature, demonstrated by an increased frequency of C:G>A:T transversions, consistent with deficient MUTYH activity. This is the first association of germline MUTYH biallelic pathogenic variants with PDAC and provides evidence of the contribution of aberrant MUTYH function to the genomic landscape of a PDAC. Detection of the base excision repair mutational signature may be a sensitive way to screen tumors for aberrant MUTYH function that can reveal potential germline MUTYH-related cancer susceptibility, and allow inference of pathogenicity of detected MUTYH variants, which may have cancer prevention and therapeutic implications. Citation Format: Kasmintan A. Schrader, Carolyn Chu’ng, Eric Zhao, Hui-li Wong, Yaoqing Shen, Martin Jones, Tom Thomson, Howard Lim, Sean Young, Carol Cremin, Robert Holt, Peter Eirew, Joanna Karasinska, Jacquie Schein, Yongjun Zhao, Andy Mungall, Richard Moore, Yussanne Ma, Alexandra Fok, Robyn Roscoe, Stephen Yip, Gillian Mitchell, Aly Karsan, Steven Jones, David Schaeffer, Janessa Laskin, Marco Marra, Daniel Renouf. Genomic analysis of pancreatic ductal adenocarcinoma in a patient with MUTYH-associated polyposis. [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 5226.

International audience; Background Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an autosomal dominant disorder predisposing humans to cutaneous and uterine leiomyomas; in 20% of affected families, type 2 papillary renal cell cancers (PRCCII) also occur with aggressive course and poor prognosis. HLRCC results from heterozygous germline mutations in the tumor suppressor fumarate hydratase (FH) gene. Methods As part of the French National Cancer Institute (INCa) "Inherited predispositions to kidney cancer" network, we performed sequence analysis and a functional study of FH in 56 families with clinically proven or suspected HLRCC and in 23 patients with isolated PRCCII (5 familial and 18 sporadic). Results We identified 32 different germline FH mutations (15 missense, six frameshifts, four nonsense, one deletion/insertion, five splice site and one complete deletion) in 40/56 (71.4%) families with proven or suspected HLRCC and in 4/23 (17.4%) probands with PRCCII alone, including 2 sporadic cases. Twenty-one of these were novel and all were demonstrated as deleterious by significant reduction of FH enzymatic activity. In addition, five asymptomatic parents in three families were confirmed as carrying disease-causing mutations. Conclusions This study identified and characterized 21 novel FH mutations and demonstrated that PRCCII can be the only one manifestation of HLRCC. Due to the incomplete penetrance of HLRCC, we propose to extend the FH mutation analysis to every patient with PRCCII occurring before 40 yrs of age or when renal tumor harbors characteristic histologic features, in order to discover previously ignored HLRCC-affected families.

Lynch syndrome is defined by the presence of germline mutations in mismatch repair (MMR) genes. Several models have been recently devised that predict mutation carrier status (Myriad Genetics, Wijnen, Barnetson, PREMM and MMRpro models). Families at moderate-high risk for harboring a Lynch-associated mutation, referred to the BC Cancer Agency (BCCA) Hereditary Cancer Program (HCP), underwent mutation analysis, immunohistochemistry and/or microsatellite testing. Seventy-two tested cases were included. Twenty-five patients were mutation positive (34.7%) and 47 were mutation negative (65.3%). Nineteen of 43 patients who were both microsatellite stable and normal on immunohistochemistry for MLH1 and MSH2 were also genotyped for mutations in these genes; all 19 were negative for MMR gene mutations. Model-derived probabilities of harboring a MMR gene mutation in the proband were calculated and compared to observed results. The area under the ROC curves were 0.75 (95%CI; 0.63-0.87), 0.86 (0.7-0.96), 0.89 (0.82-0.97), 0.89 (0.81-0.98) and 0.93 (0.86-0.99) for the Myriad, Barnetson, Wijnen, MMRpro and PREMM models, respectively. The Amsterdam II criteria had a sensitivity and specificity of 0.76 and 0.74, respectively, in this cohort. The PREMM model demonstrated the best performance for predicting carrier status based on the positive likelihood ratios at the >10%, >20% and >30% probability thresholds. In this referred cohort, the PREMM model had the most favorable concordance index and predictive performance for carrier status based on the positive LR. These prediction models (PREMM, MMRPro and Wijnen) may soon replace the Amsterdam II and revised Bethesda criteria as a prescreening tool for Lynch mutations.

Dyskeratosis Congenita (DC) is a marrow failure syndrome characterized by skin and nail abnormalities, oral leukoplakia and very short telomeres in circulating leukocytes. Heritable defects in telomere maintenance have been directly implicated in DC by the discovery of mutations in genes encoding components of the telomerase complex: DKC1, TERT, and TERC as well as mutations in the gene encoding the telomere binding protein TINF2. Defective telomeres in DC result in impaired hematopoiesis and predispose to myeloproliferative disorders. Heritable mutations in TERT and TERC have also been implicated in patients presenting with aplastic anemia (AA) and idiopathic pulmonary fibrosis (IPF) without clinical signs of DC. Because short telomeres appear to be associated with increased risks for various human cancers, including head and neck cancer, we sequenced TERT and TERC in two patients with oral carcinoma and anemia. The first patient presented at age 47 with invasive squamous cell carcinoma (SCC) of the tongue. The patient had a male sibling said to be also suffering from SCC which was not available for analysis and his mother died at age 37 from lymphoma. The patient displayed mild macrocytic anemia and oral leukoplakia. The telomere lengths of peripheral blood cells from the patient, determined by flow-FISH, were found to be below the first percentile expected for his age. In contrast, the leukocyte telomere lengths for the patient’s father and a female sibling were within the normal range. Bi-directional sequence analysis of TERT and TERC was conducted on DNA isolated from whole blood for the three family members. A novel mutation in exon 9 of TERT, C842T, situated within the reverse transcriptase domain of the telomerase enzyme catalytic component was identified in the patient but not in the 2 unaffected relatives. This suggested inheritance of a TERT mutation from the mother. The function of TERT C842T was compared to wildtype (WT) TERT by transfecting WT and mutant TERT cDNA into clonal Jurkat T cells and measuring telomere elongation by flow-FISH following 4 weeks of culture. TERT C842T showed 30% of the elongation obtained with WT TERT (p=0.0034). The second patient is a 60 yr old male with SCC of the tongue and refractory anemia with ring sideroblasts. The leukocyte telomere length was around the 1st percentile expected for his age. TERT sequencing revealed a three nucleotide deletion resulting in loss of 441E while retaining frame that is expected to impair telomerase activity. Our data support the concept that mutations in TERT can cause defective telomere maintenance and thereby compromise the proliferation of hematopoietic as well as epithelial cells. The resulting loss of normal cells selects for cells with defective DNA damage checkpoints that are triggered by chromosome ends without telomere repeats. Such cells are at high risk of becoming malignant because their proliferation will be stimulated by the loss of normal cells and their genome is very unstable as telomere function is compromised. Together these factors facilitate and enable clonal evolution of abnormal cells by DNA repair defects and cycles of chromosome fusions/bridge/breakage. Hematological and pathological findings consistent with Dyskeratosis Congenita together with peripheral blood telomere length measurements appear useful parameters to screen for telomere defects in patients and facilitate the discovery of mutations in “telomere maintenance” genes. The TERT mutations in patients with oral carcinomas illustrate that disease manifestations of telomere dysfunction in humans can be very diverse and range from DC, to defective hematopoiesis, pulmonary fibrosis and cancer predisposition.

Background With a population of approximately 4.380 million people and an estimated Lynch syndrome mutation prevalence of 1/531, there are an expected 8000 individuals with Lynch syndrome in British Columbia. The Hereditary Cancer Program (HCP) of the BC Cancer Agency (BCCA) has provided clinical testing for Lynch syndrome since 2004 to patients across the province. Currently, there are approximately 100 patients with confirmed Lynch syndrome mutations in the BCCA database. Potential obstacles in ascertaining Lynch syndrome through a traditional clinic-based approach include physician awareness of referral criteria, patient's lack of knowledge of cancer family history, patient compliance, and availability of tumour tissue for testing. Given these obstacles, a population based approach to identifying Lynch syndrome through incident testing of newly diagnosed colorectal cancers under age 50 by microsatellite instability testing (MSI) was launched in BC in June of 2008.