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Mosaic variants are regularly detected on hereditary cancer genetic tests. While some of these variants may be constitutional, the majority are likely limited to blood lineages. In the present study, we correlate clinical histories from individuals with mosaic findings identified on hereditary cancer testing and the outcomes of follow-up fibroblast (FB) testing. We observed 620 mosaic variants, including 339 pathogenic or likely pathogenic variants (PVs) occurring most often in TP53, CHEK2, ATM, and NF1. About half of individuals with NF1 mosaic PVs did not report any clinical features of NF1 and were older at testing (p0.0001) compared to those with an NF1-related phenotype. Among 42 mosaic PVs evaluated by FB testing, 17 (40.5%) were confirmed in FB and were mostly identified in individuals with phenotypes consistent with the gene disease spectrum. Our data show that FB testing is helpful for identifying those with likely constitutional mosaicism benefitting from increased screening and follow-up vs. those with blood-limited variants potentially not requiring intense surveillance but warranting further hematologic work-up.

Purpose:The identification of variants of uncertain significance (VUS) in the BRCA1 and BRCA2 genes by hereditary cancer testing poses great challenges for the clinical management of variant carriers. The ACMG/AMP (American College of Medical Genetics and Genomics/Association for Molecular Pathology) variant classification framework, which incorporates multiple sources of evidence, has the potential to establish the clinical relevance of many VUS. We sought to classify the clinical relevance of 133 single-nucleotide substitution variants encoding missense variants in the DNA-binding domain (DBD) of BRCA2 by incorporating results from a validated functional assay into an ACMG/AMP-variant classification model from a hereditary cancer–testing laboratory.Experimental Design:The 133 selected VUS were evaluated using a validated homology-directed double-strand DNA break repair (HDR) functional assay. Results were combined with clinical and genetic data from variant carriers in a rules-based variant classification model for BRCA2.Results:Of 133 missense variants, 44 were designated as non-functional and 89 were designated as functional in the HDR assay. When combined with genetic and clinical information from a single diagnostic laboratory in an ACMG/AMP-variant classification framework, 66 variants previously classified by the diagnostic laboratory were correctly classified, and 62 of 67 VUS (92.5%) were reclassified as likely pathogenic (n = 22) or likely benign (n = 40). In total, 44 variants were classified as pathogenic/likely pathogenic, 84 as benign/likely benign, and 5 remained as VUS.Conclusions:Incorporation of HDR functional analysis into an ACMG/AMP framework model substantially improves BRCA2 VUS re-classification and provides an important tool for determining the clinical relevance of individual BRCA2 VUS.

Supplementary Table from Classification of BRCA2 Variants of Uncertain Significance (VUS) Using an ACMG/AMP Model Incorporating a Homology-Directed Repair (HDR) Functional Assay

Purpose: The identification of variants of uncertain significance (VUS) in the BRCA1 and BRCA2 genes by hereditary cancer testing poses great challenges for the clinical management of variant carriers. The ACMG/AMP (American College of Medical Genetics and Genomics/Association for Molecular Pathology) variant classification framework, which incorporates multiple sources of evidence, has the potential to establish the clinical relevance of many VUS. We sought to classify the clinical relevance of 133 single-nucleotide substitution variants encoding missense variants in the DNA-binding domain (DBD) of BRCA2 by incorporating results from a validated functional assay into an ACMG/AMP-variant classification model from a hereditary cancer–testing laboratory. Experimental Design: The 133 selected VUS were evaluated using a validated homology-directed double-strand DNA break repair (HDR) functional assay. Results were combined with clinical and genetic data from variant carriers in a rules-based variant classification model for BRCA2. Results: Of 133 missense variants, 44 were designated as non-functional and 89 were designated as functional in the HDR assay. When combined with genetic and clinical information from a single diagnostic laboratory in an ACMG/AMP-variant classification framework, 66 variants previously classified by the diagnostic laboratory were correctly classified, and 62 of 67 VUS (92.5%) were reclassified as likely pathogenic (n = 22) or likely benign (n = 40). In total, 44 variants were classified as pathogenic/likely pathogenic, 84 as benign/likely benign, and 5 remained as VUS. Conclusions: Incorporation of HDR functional analysis into an ACMG/AMP framework model substantially improves BRCA2 VUS re-classification and provides an important tool for determining the clinical relevance of individual BRCA2 VUS.

We aimed to determine whether monoallelic MUTYH pathogenic and likely pathogenic variants (PVs) are associated with colorectal, breast, and endometrial cancer. Cases were individuals with colorectal, female breast, or endometrial cancer who reported European ancestry alone and underwent a multi-gene hereditary cancer panel at a large reference laboratory. Controls were individuals of European (non-Finnish) descent from GnomAD with cancer cohorts removed. We performed a Fisher's exact test to generate odds ratios (ORs) with 95% confidence intervals (CI). Prevalence of single MUTYH PVs in cancer cohorts versus controls, respectively, was: colorectal cancer, 2.1% vs. 1.8% (OR 1.2, 95% CI 0.99-1.5, p = 0.064); breast cancer 1.9% vs. 1.7% (OR 1.1, 95% CI 0.96-1.3, p = 0.15); and endometrial cancer, 1.7% vs. 1.7% (OR 0.98; 95% CI 0.70-1.3, p = 0.94). Using the largest colorectal and endometrial cancer cohorts and one of the largest breast cancer cohorts from a single case-control study, we did not observe a significant difference in the prevalence of monoallelic MUTYH PVs in these cohorts compared to controls. Additionally, frequencies among cancer cohorts were consistent with the published MUTYH carrier frequency of 1-2%. These findings suggest there is no association between colorectal, endometrial, or breast cancer and MUTYH heterozygosity in individuals of European ancestry.

Purpose Although CHEK2 is a well-established cancer gene, questions remain including whether risks vary substantially between different variants and whether biallelic carriers have higher risks than heterozygotes. We report on a cohort of individuals with CHEK2 pathogenic and likely pathogenic variants (collectively, PV) in order to better characterize this gene. Methods We retrospectively queried samples submitted for multi-gene hereditary cancer testing to identify individuals with CHEK2 PVs and assessed differences in phenotypes among various genotypes. Results CHEK2 PVs were identified in 2,508 individuals, including 32 individuals with biallelic CHEK2 PVs. Breast (female, 59.9% and male, 11.8%), prostate (20.1%), and colorectal (3.5%), were among the most frequently reported cancers. Select missense PVs showed similar cancer prevalence to truncating PVs while some others showed lower prevalence. No significant differences were observed between biallelic carriers and heterozygotes. Conclusions Our data support that some, but not all, CHEK2 missense PVs demonstrate lower cancer prevalence; further studies are needed to continue characterizing possible variant specific risks. In addition, biallelic CHEK2 PVs do not appear to be associated with a more severe phenotype than single CHEK2 PVs. Furthermore, co-occurrences with PVs in other cancer risk genes are common among CHEK2 heterozygotes and often warrant additional management.

Purpose An association of Lynch syndrome (LS) with breast cancer has been long suspected; however, there have been insufficient data to address this question for each of the LS genes individually. Methods We conducted a retrospective review of personal and family history in 423 women with pathogenic or likely pathogenic germ-line variants in MLH1 (N = 65), MSH2 (N = 94), MSH6 (N = 140), or PMS2 (N = 124) identified via clinical multigene hereditary cancer testing. Standard incidence ratios (SIRs) of breast cancer were calculated by comparing breast cancer frequencies in our study population with those in the general population (Surveillance, Epidemiology, and End Results 18 data). Results When evaluating by gene, the age-standardized breast cancer risks for MSH6 (SIR = 2.11; 95% confidence interval (CI), 1.56–2.86) and PMS2 (SIR = 2.92; 95% CI, 2.17–3.92) were associated with a statistically significant risk for breast cancer whereas no association was observed for MLH1 (SIR = 0.87; 95% CI, 0.42–1.83) or MSH2 (SIR = 1.22; 95% CI, 0.72–2.06). Conclusion Our data demonstrate that two LS genes, MSH6 and PMS2, are associated with an increased risk for breast cancer and should be considered when ordering genetic testing for individuals who have a personal and/or family history of breast cancer.

Background Genes in the homologous recombination pathway have shown varying results in the literature regarding ovarian cancer (OC) association. Recent case-control studies have used allele counts alone to quantify genetic associations with cancer. Methods A retrospective case-control study was performed on 6,182 women with OC referred for hereditary cancer multi-gene panel testing (cases) and 4,690 mothers from trios who were referred for whole-exome sequencing (controls). We present age-adjusted odds ratios (ORAdj) to determine association of OC with pathogenic variants (PVs) in homologous recombination genes. Results Significant associations with OC were observed in BRCA1, BRCA2, RAD51C and RAD51D. Other homologous recombination genes, BARD1, NBN, and PALB2, were not significantly associated with OC. ATM and CHEK2 were only significantly associated with OC by crude odds ratio (ORCrude) or by ORAdj, respectively. However, there was no significant difference between ORCrude and ORAdj for these two genes. The significant association of PVs in BRIP1 by ORCrude (2.05, CI = 1.11 to 3.94, P = 0.03) was not observed by ORAdj (0.87, CI = 0.41 to 1.93, P = 0.73). Interestingly, the confidence intervals of the two effect sizes were significantly different (P = 0.04). Conclusion The lack of association of PVs in BRIP1 with OC by ORAdj is inconsistent with some previous literature and current management recommendations, highlighted by the significantly older age of OC onset for BRIP1 PV carriers compared to non-carriers. By reporting ORAdj, this study presents associations that reflect more informed genetic contributions to OC when compared to traditional count-based methods. Electronic supplementary material The online version of this article (10.1186/s13053-019-0119-3) contains supplementary material, which is available to authorized users.

IMPORTANCE: CDH1 pathogenic variants have been estimated to confer a 40% to 70% and 56% to 83% lifetime risk for gastric cancer in men and women, respectively. These are likely to be overestimates owing to ascertainment of families with multiple cases of gastric cancer. To our knowledge, there are no penetrance estimates for CDH1 without this ascertainment bias. OBJECTIVE: To estimate CDH1 penetrance in a patient cohort not exclusively ascertained based on strict hereditary diffuse gastric cancer (HDGC) criteria. DESIGN, SETTING, AND PARTICIPANTS: Retrospective review of 75 families found to have pathogenic variants in CDH1 through clinical ascertainment and multigene panel testing at a large commercial diagnostic laboratory from August 5, 2013, to June 30, 2018. CDH1 pathogenic variants were identified in 238 individuals from 75 families. Pedigrees from those families included cancer status for 1679 relatives. Penetrance estimates are based on 41 families for which completed pedigrees were available. MAIN OUTCOMES AND MEASURES: Gastric cancer standardized incidence ratio estimates relative to Surveillance, Epidemiology, and End Results (SEER) Program incidence for pathogenic CDH1 variants from families ascertained without regard to HDGC criteria. RESULTS: Among the 238 individuals with a CDH1 pathogenic variant, mean (SD) age was 49.3 (18.1) years and 63.4% were female. Ethnicity was reported for 67 of 75 (89%) families; of these 67 families, 51 (76%) reported European ancestry, whereas Asian, African, Latino, and 2 or more ancestries were reported for 4 families (6%) each. Standardized incidence ratios for gastric and breast cancer were significantly elevated above SEER incidence. Extrapolated cumulative incidence of gastric cancer at age 80 years was 42% (95% CI, 30%-56%) for men and 33% (95% CI, 21%-43%) for women with pathogenic variants in CDH1, whereas cumulative incidence of female breast cancer was estimated at 55% (95% CI, 39%-68%). International Gastric Cancer Linkage Consortium criteria were met in 25 of the 75 (33%) families; however, dispensing with the requirement of confirmation of HDGC histologic subtype, 43 (57%) would meet criteria. CONCLUSIONS AND RELEVANCE: The cumulative incidence of gastric cancer for individuals with pathogenic variants in CDH1 is significantly lower than previously described. Because prophylactic gastrectomy can have bearing upon both physical and psychological health, further discussion is warranted to assess whether this surgical recommendation is appropriate for all individuals with pathogenic variants in CDH1.

The recognition of genes implicated in ovarian cancer risk beyond BRCA1, BRCA2, and the Lynch syndrome genes has increased the variety of testing options available to providers and patients. We report the frequency of pathogenic variants identified among individuals with ovarian cancer undergoing clinical genetic testing via a multi-gene hereditary cancer panel.Genetic testing of up to 32 genes using a hereditary cancer panel was performed on 4439 ovarian cancer cases, and results were analyzed for frequency of pathogenic variants. Statistical comparisons were made using t-tests and Fisher's exact tests.The positive yield was 13.2%. While BRCA1/2 pathogenic variants were most frequent, one third (33.7%) of positive findings were in other homologous recombination genes, and accounted for over 40.0% of findings in endometrioid and clear cell cases. Women with a personal history of breast cancer (22.1%), who reported a family history of ovarian cancer (17.7%), and/or serous histology (14.7%) were most likely to harbor a pathogenic variant. Those with very early onset (30 years) and late onset (≥70 years) ovarian cancer had low positive yields.Our study highlights the genetic heterogeneity of ovarian cancer, showing that a large proportion of cases are not due to BRCA1/2 and the Lynch syndrome genes, but still have an identifiable hereditary basis. These findings substantiate the utility of multi-gene panel testing in ovarian cancer care regardless of age at diagnosis, family history, or histologic subtype, providing evidence for testing beyond BRCA1/2 and the Lynch syndrome genes.

Purpose: Germ-line testing for panels of cancer genes using next-generation sequencing is becoming more common in clinical care. We report our experience as a clinical laboratory testing both well-established, high-risk cancer genes (e.g., BRCA1/2, MLH1, MSH2) as well as more recently identified cancer genes (e.g., PALB2, BRIP1), many of which have increased but less well-defined penetrance. Genet Med 18 8, 823–832. Methods: Clinical genetic testing was performed on over 10,000 consecutive cases referred for evaluation of germ-line cancer genes, and results were analyzed for frequency of pathogenic or likely pathogenic variants, and were stratified by testing panel, gene, and clinical history. Genet Med 18 8, 823–832. Results: Overall, a molecular diagnosis was made in 9.0% of patients tested, with the highest yield in the Lynch syndrome/colorectal cancer panel. In patients with breast, ovarian, or colon/stomach cancer, positive yields were 9.7, 13.4, and 14.8%, respectively. Approximately half of the pathogenic variants identified in patients with breast or ovarian cancer were in genes other than BRCA1/2. Genet Med 18 8, 823–832. Conclusion: The high frequency of positive results in a wide range of cancer genes, including those of high penetrance and with clinical care guidelines, underscores both the genetic heterogeneity of hereditary cancer and the usefulness of multigene panels over genetic tests of one or two genes. Genet Med 18 8, 823–832.

Introduction: Expansion of genetic testing technologies has brought multi-gene panels for cancer susceptibility into the clinic; however, the clinical utility of these next-generation sequencing (NGS) panels is largely unknown. Hypothesis: We hypothesized that the use of multi-gene panels would yield a significant number of cases with more than one pathogenic variant. Methods: We retrospectively queried oncology tests reported at GeneDx from August 2013 to April 2014 for individuals with more than one pathogenic variant. Next, we calculated the proportion of individuals with more than one pathogenic variant among all positive reports, excluding familial and stand-alone BRCA1/2 tests. We then extracted personal and family histories, including available segregation data, to categorize the phenotypes. Results: Of 406 unique, unrelated individuals with pathogenic or likely pathogenic findings, 11 (2.7%) had more than one pathogenic variant. This total includes nine individuals with a mutation in more than one gene, as well as two individuals with two mutations in trans in the same gene. Ten of these 11 individuals were identified by multi-gene panel tests, one individual by step-wise (tiered) testing. Seven of 11 individuals were positive for a pathogenic variant in a traditional, highly-penetrant cancer susceptibility gene and another pathogenic variant in a gene with moderate cancer susceptibility, such as CHEK2 and ATM. Three of 11 probands had more than one primary tumor. Several of the families were significant for bilineal cancer risk. Conclusions: Our data suggest that a traditional single gene approach to cancer testing may fail to identify all pathogenic variants related to the clinical presentation. The identification of a second risk factor for inherited susceptibility to cancer allows for appropriate testing and management considerations for family members. In conclusion, we provide early evidence for the consideration of multi-gene panel testing in a clinical oncology setting. Citation Format: Rachel Nusbaum, Lisa Susswein, Kathleen Hruska, Melanie Hussong, Windy Berkofsky-Fessler, Mingjuan Liao, Erica Rinella, Nina Sanapareddy, Joaquin Villar, Haiyan Wan, Zhixiong Xu, Rebecca Y Bassett, Elisabeth McKeen, Constance Murphy, Deborah Pencarinha, Jessica Booker, Maria L Cremona, Patricia Murphy, Rachel T Klein. Individuals with more than one pathogenic variant: Rationale for considering multi-gene panel testing for cancer susceptibility [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-12-05.

668 Background: Approximately 25% of pheochromocytomas (PCC) have a hereditary basis, and germline variants in the SDHA, SDHB, SDHC, SDHD, SDHAF2, TMEM127, MAX, VHL, FH, RET, MEN1, and NF1 genes have been associated with a predisposition to PCC and paraganglioma (PGL). Multi-gene hereditary cancer panel testing for PCC has become increasingly more common than single-gene testing algorithms. Identification of a pathogenic or likely pathogenic variant (PV/LPV) in one of these genes has important implications for surveillance in patients and their family members. Here we describe the spectrum of PV/LPV variants identified in individuals with PCC. Methods: We performed a retrospective review of clinical and molecular data for all individuals diagnosed with PCC who underwent panel testing through BioReference Laboratories that included at least SDHA, SDHB, SDHC, SDHD, SDHAF2, TMEM127, MAX, VHL, FH, RET, MEN1, and NF1 between January 2016 and February 2017. Results: Seventy-nine individuals underwent testing due to a personal (n = 76) or family (n = 3) history of PCC. The positive yield was 14% (11/79). The majority of PV/LPV were in SDHB (n = 4; 36%), followed by RET (n = 2, 18%), with the remaining variants being identified in SDHA (1), SDHC (1), VHL (1), TMEM127 (1), and MAX (1). Approximately half (6/11) of those with a PV/LPV had a non-syndromic presentation of a unilateral PCC with no reported family history of PCC or PGL. The average age at tumor diagnosis was lower for probands testing positive than those without PV/LPV (34y±14 vs 44y±16). Conclusions: Our data support previous recommendations that patients with apparently sporadic, non-syndromic PCC be considered for genetic testing. Panel testing is a useful tool for identifying individuals with hereditary PCC.

596 Background: Lynch syndrome (LS), also known as hereditary non-polyposis colorectal cancer (HNPCC), is a hereditary colorectal cancer syndrome thought to present with few or no polyps. It has been suggested that the majority of LS patients with colon polyps will develop 1-9 cumulative adenomatous polyps in their lifetime, while approximately 10% will develop ≥10. Our aim was to describe polyp burden in a cohort of LS patients who were ascertained via multi-gene cancer panel testing. Methods: We retrospectively reviewed the personal history for all individuals with a pathogenic or likely pathogenic variant (collectively, PV) in MLH1, MSH2 (including 3’ EPCAM deletions), MSH6, or PMS2. Individuals with more than one PV in a LS-associated or other gene were excluded. All polyp data was obtained from provided test requisition forms and/or pathology reports. Results: A total of 131 individuals reported to have colon polyps were molecularly confirmed as having LS. Of these individuals, 55% (72/131) reported a history of colorectal cancer. Overall, polyp burden was reported as follows: 83% (109/131) with 1-10 polyps, 13% (17/131) with 10-19 polyps, and 4% (5/131) with 20-50 polyps. Of the 5 individuals reporting 20-50 polyps, the average was 31.2 polyps (range 21-50). Adenomatous pathology was reported for one or more polyps in 69% (91/131) of individuals. When limited to those with adenomatous polyps, 85% (77/91) reported 1-10 polyps, 11% (10/91) reported 10-19 polyps, and 4% (4/91) reported 20-50 polyps. When breaking down by presence and absence of colorectal cancer, 18% (13/72) and 15% (9/59), respectively, reported a polyp burden ≥10. Overall, 17% (22/131) of all LS patients reported ≥10 polyps. Conclusions: Similar to previously published data, the majority of LS patients with colon polyps report a polyp burden of < 10. However, our data suggest that the proportion of LS patients with a polyp burden of ≥10 may be higher than previously reported (17% vs. 10%) stressing the importance of including the LS-associated genes for these patients. While LS has historically been referred to as a “non-polyposis” syndrome, a subset of patients actually present with an attenuated polyposis-like phenotype.

576 Background: Young age at onset is a hallmark feature of an inherited predisposition to cancer. Recent evidence suggests that the incidence of pathogenic/likely pathogenic variants (PV) in cancer predisposition genes among individuals diagnosed with colorectal cancer (CRC) ≤ age 35 is high, but few studies have examined the frequency identified by multi-gene hereditary cancer panel testing. We report on PV yield and clinical presentation of individuals diagnosed with CRC ≤ 35 years (y). Methods: We retrospectively reviewed test requisition forms and provided pathology reports for 4,727 individuals with CRC who underwent panel testing of, at a minimum, MLH1, MSH2, MSH6, PMS2, EPCAM, APC, and MUTYH. Two-tailed Fisher’s exact tests were used to determine statistically significant differences between groups. Results: Of the 691 individuals diagnosed with CRC ≤35y, 137 PV were identified in 126 individuals (126/691, 18.2%), including 72 with Lynch syndrome, 16 with familial adenomatous polyposis (FAP), five with MUTYH-associated polyposis, four with constitutional mismatch repair deficiency, one with juvenile polyposis syndrome, and one with Peutz-Jeghers syndrome. Thirty-eight additional PVs were identified in other non-CRC genes. Microsatellite instability (MSI) and immunohistochemistry (IHC) results were reported for 277 individuals and were reportedly abnormal in 63. The yield of PV in individuals with abnormal tumor studies was 52.4% (33/63); PV in genes other than the Lynch syndrome-associated genes were identified, commonly in the MSI-H group. While statistical significance was not observed, the positive rate was higher for individuals with non-rectal cancers (colon cancer: 104/534, 19.5%; rectal cancer: 22/157, 14.0%, p = 0.13). Conclusions: In our cohort, 18.2% of individuals diagnosed with CRC ≤35y were found to harbor a PV. Yield increased in those with abnormal MSI/IHC as well as non-rectal tumor location. Hereditary predispositions in patients diagnosed with very early-onset CRC are not limited to Lynch syndrome and FAP. Therefore, individuals with very early-onset CRC may benefit from multi-gene panel testing rather than syndromic-based testing.

1518 Background: In multi-gene hereditary cancer testing, multiple syndromes may be interrogated simultaneously, increasing the likelihood of detecting an underlying cancer predisposition. We characterized the yield and distribution of pathogenic or likely pathogenic variants (PV/LPV) in patients with a personal history of sarcoma undergoing panel testing through our clinical diagnostic laboratory. Methods: We retrospectively reviewed panel test results, demographic data, and personal/family history information from patients reporting a personal history of sarcoma. Patients included in this study underwent panel testing (NGS and del/dup) of up to 61 genes at this laboratory and concurrent or prior TP53 analysis at this or an outside laboratory. Chi-square and Fisher’s exact tests were used to compare groups. Results: Among 374 sarcoma patients, 53 (14.2%) harbored one or more PV/LPV in 14 genes: TP53, BRCA2, CHEK2, BRCA1, ATM, MSH6, MLH1, NBN, BAP1, BRIP1, FLCN, MSH2, PTEN, and RB1. Thirty-nine (10.4%) individuals reported both a personal and family history of sarcoma; however, PV/LPV were not more likely to be detected among this group than those with personal history alone (p = 1.0). PV/LPV were most often detected in BRCA1/2 (15/374, 4.0%) or TP53 (12/374, 3.2%). Notably, four probands with BRCA1/2 PV/LPV reported a family history of sarcoma, including one kindred in which the variant was present in two brothers, both affected with sarcoma. Additionally, seven patients were found to have PV/LPV (1.9%) in genes causative for Lynch syndrome. Among patients with PV/LPV in genes other than TP53, nearly half (17/41, 41.5%) met National Comprehensive Cancer Network TP53 testing criteria. Conclusions: The majority of PV/LPV were identified in genes for which association with sarcoma risk is not well-established. While several of these genes have been implicated in somatic pathways related to sarcoma development, it is unclear whether these germline findings are causative, play no role, or modify sarcoma risk. Although these data do not inherently associate non- TP53 genes with sarcoma risk, they suggest a potential clinical benefit can be gained from performing hereditary cancer risk assessment and multi-gene panel testing in sarcoma patients.

244 Background: Pancreatic ductal adenocarcinoma (PC) is associated with multiple hereditary cancer syndromes. Genes implicated in hereditary PC include ATM, BRCA1, BRCA2, CDKN2A, EPCAM, MLH1, MSH2, MSH6, PALB2 and PMS2. The advent of multi-gene hereditary cancer panel testing streamlines diagnoses and medical management for clinicians and patients. Our objective was to assess the yield of pathogenic/likely pathogenic variants (PV/LPV) in individuals with PC undergoing panel testing as an initial test at GeneDx. Methods: We retrospectively reviewed panel test results of 605 individuals reporting a personal history of PC. Panel testing evaluated up to 32 genes associated with hereditary cancer. Individuals reporting neuroendocrine pathology or previous BRCA1/BRCA2 testing were excluded. Results: In this cohort, 61 PV/LPV were detected in 57 individuals in the following genes: ATM (17), BRCA2 (14), BRCA1 (5), CDKN2A (5), PALB2 (5), CHEK2 (4), MLH1 (2), MUTYH (2), PMS2 (2), BARD1 (1), FANCC (1), MSH2 (1), RAD51D (1) and TP53 (1), corresponding to a positive yield of 9.4% (57/605). Fifty-one of 61 PV/LPV were detected in genes associated with PC (84%) while 10 PV/LPV (16%) were identified in other genes including BARD1, CHEK2, FANCC, MUTYH, and RAD51D. The diagnostic yield among those reporting a family history of PC (33/294, 11.2%) was not statistically different from those without a reported family history (24/311, 7.7%). However, PV/LPV in ATM were detected more often in individuals reporting a family history of PC compared to those without a family history (4.1% vs. 1.6%, p=0.018). Conclusions: In total, 9.4% of patients with PC tested positive for PV/LPV in 14 different genes by panel testing. Although the majority of PV/LPV were identified in known PC genes, 16% of positive findings occurred in genes not typically associated with PC. ATM was most commonly implicated and more frequently reported in patients reporting family histories of PC. Assessing whether these genes are indeed causally related to PC and/or are possibly associated with other cancer types requires further investigation. Based on our results we conclude multi-gene panel testing may be considered as a first option for patients with PC regardless of their family history.