Citations

Abstract Background For many evidence criteria within v3.0 of the ACMG/AMP guidelines, methodologies have been developed to empower their use outside the stipulated evidence strengths. However, no such methodology has been established for case-control data (PS4). With the release of large-scale unselected case-control datasets and expansion of nationally-collected laboratory datasets enriched for pathogenic variant carriers, there is potential to combine datasets across ascertainment contexts in a more quantitative manner using novel likelihood ratio tools. Methods Using our published PS4-LR-Calculator, we calculated a combined log likelihood ratio (PS4-LLR) across five datasets (three unselected, and two enriched), and estimated enrichment of pathogenic variants in clinically-ascertained laboratory data using truncating variant prevalence. Results Data were combined for 10,817 missense variants from 325,345 female breast cancer patients and 671,006 controls of Western European ancestry for five breast cancer susceptibility genes ( BRCA1, BRCA2, PALB2, ATM, CHEK2 ). A combined LLR was produced for 4,690 missense variants; 927 variants received evidence towards pathogenicity (LLR≥ 1), and 3,242 received evidence towards benignity (LLR≤ -1). Conclusion This flexible, variant-level methodology combines nationally-collected ‘enriched’ datasets with unselected case-control cohorts, expanding the available information for case-control analysis, boosting power, enabling exploration of atypical penetrance and empowering variant classification.

Abstract Purpose: To determine the relationship between germline pathogenic variants (PV) in cancer predisposition genes and the risk of ductal carcinoma in situ (DCIS). Experimental Design: Germline PV frequencies in breast cancer predisposition genes (ATM, BARD1, BRCA1, BRCA2, CDH1, CHEK2, PALB2, RAD51C, and RAD51D) were compared between DCIS cases and unaffected controls and between DCIS and invasive ductal breast cancer (IDC) cases from a clinical testing cohort (n = 9,887), a population-based cohort (n = 3,876), and the UK Biobank (n = 2,421). The risk of contralateral breast cancer (CBC) for DCIS cases with PV was estimated in the population-based cohort. Results: Germline PV were observed in 6.5% and 4.6% of women with DCIS in the clinical testing and population-based cohorts, respectively. BRCA1, BRCA2, and PALB2 PV frequencies were significantly lower among women with DCIS than those with IDC (clinical cohort: 2.8% vs. 5.7%; population-based cohort: 1.7% vs. 3.7%), whereas the PV frequencies for ATM and CHEK2 were similar. ATM, BRCA1, BRCA2, CHEK2, and PALB2 PV were significantly associated with an increased risk of DCIS (OR > 2.0), but only BRCA2 PV were associated with high risk (OR > 4) in both cohorts. The cumulative incidence of CBC among carriers of PV in high-penetrance genes with DCIS was 23% over 15 years. Conclusions: The enrichment of PV in ATM, BRCA1, BRCA2, CHEK2, and PALB2 among women with DCIS suggests that multigene panel testing may be appropriate for women with DCIS. Elevated risks of CBC in carriers of PV in high-penetrance genes with DCIS confirmed the utility of testing for surgical decision-making.

10511 Background: Germline BRCA2 loss-of function (LOF) variants identified by clinical genetic testing predispose to breast, ovarian, prostate and pancreatic cancer. However, variants of uncertain significance (VUS) (n > 4000) limit the clinical use of testing results. Thus, there is an urgent need for functional characterization and clinical classification of all BRCA2 variants. Here we report on comprehensive saturation genome editing (SGE)-based functional characterization of 97% of all possible single nucleotide variants (SNVs) in the BRCA2 DNA Binding Domain hotspot encoded by exons 15 to 26 for pathogenic missense variants. Methods: SGE of exons 15 to 26 of BRCA2(MANE transcript ENST00000380152.8) was performed in the haploid human HAP1 cell line. Each exon along with 10bp flanking intronic sequence was studied as an independent target region. The most efficient sgRNA for each target region was selected and cloned into a Cas9 expressing plasmid. Site-saturation mutagenesis (SSM) libraries for each of the 14 target regions were designed to target every nucleotide and were generated by site directed mutagenesis using NNN-tailed PCR primers. HAP1 cells were transfected and harvested at Day5 and 14. Cell survival in response to each variant was assessed based on deep sequence analysis of the surviving endogenously targeted HAP1 cells at Day 5 and Day 14. Results: A total of 7013 SNVs were characterized as functionally abnormal (n = 955), intermediate/uncertain, or functionally normal (n = 5224) based on 95% precision for ClinVar known pathogenic and benign standards. Results were validated relative to batches of nonsense and synonymous variants and variants evaluated using a homology directed repair (HDR) functional assay. Breast cancer case-control association studies showed that pooled SNVs encoding functionally abnormal missense variants were associated with increased risk of breast cancer (odds ratio (OR) 3.89, 95%CI: 2.77-5.51). The functional data were added to other sources of information in a ClinGen/ACMG/AMP-like model and 700 functionally abnormal SNVs, including 220 missense SNVs, were classified as pathogenic or likely pathogenic, while 4862 functionally normal SNVs, including 3084 missense SNVs, were classified as benign or likely benign. Conclusions: The production of functional maps for 97% of all SNVs in the BRCA2 DBD allowed for separation of nucleotide/protein-level functional aberrations. When coupled with genetic and clinical sources of evidence this study led to clinical classification of 5500 individual variants. These data will prove useful in the future, through integration with other datasets, for characterization and clinical classification of all variants in this region in individuals from all racial and ethnic backgrounds and for all BRCA2 associated forms of cancer.

Abstract Despite the current binary clinical classification of variants (pathogenic versus benign), it is widely recognized that risk is a continuum. Prior studies have suggested the existence of reduced penetrance pathogenic variants (RPPVs), which pose challenges for identification, reporting, patient counseling and care. Through the current study, we sought to establish RPPVs as a new category of variants, with efforts focused specifically on BRCA1 and BRCA2 (BRCA). We compiled, compared, and assessed data for BRCA RPPVs from two large clinical diagnostic laboratories to establish an initial set of reduced penetrance pathogenic variants. Specifically, candidate BRCA RPPVs provided by clinical diagnostic laboratories were compiled to identify those with the highest prior likelihood of being a RPPV, based on concordant interpretations. Evidence of reduced penetrance included: 1) the identification of biallelic Fanconi Anemia-affected carriers; 2) splicing, missense, and nonsense-mediated RNA decay (NMD)-escaping variants; 3) laboratory-validated cancer history weighting models; 4) published variant-specific risk estimation data; 5) extrapolation of a reduced-risk interpretation onto close match variants that are expected to have the same effect; and 6) functional data. Sixteen candidate BRCA RPPV present in both lists from both laboratories were systematically assessed. For BRCA1, variants included c.5096G>A p.(Arg1699Gln) and variants impacting the canonical c.671 splice acceptor site. For BRCA2, variants included three frameshift (c.658_658delGT, c.9672dupA, c.9699_9702delTATG), two spliceogenic (c.8488-1G>A and c.8488-1G>T), and three missense (c.7878G>C, T, p.(Trp2626Cys); and c.9302T>G p.(Leu3101Arg)) variants. Our study is the first to clearly evaluate and establish BRCA RPPVs as a new class of variants, based on consistency in results across 16 variants using different interpretation strategies between laboratories. These variants impart a moderately increased risk of breast cancer, often considered to be between 2-4 fold, which should be considered when determining risk-informed cancer prevention strategies. Furthermore, our study establishes a framework to harmonize interpretation and standardize reporting of BRCA RPPV, by providing evidence to support this new classification for 16 variants. Further work to define clinically meaningful risk thresholds and categories for reporting BRCA RPPV are needed to personalize cancer risks in conjunction with other risk factors. Citation Format: Tuya Pal, Erin Mundt, Marcy Richardson, Elizabeth Chao, Tina Pesaran, Thomas P. Slavin, Fergus Couch, Alvaro N. Monteiro. Reduced penetrance BRCA1 and BRCA2 pathogenic variants in clinical germline genetic testing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6615.

Abstract The success of precision cancer prevention and treatment hinges on accurate discrimination between benign and pathogenic germline alleles in cancer susceptibility genes. Variants of uncertain clinical significance (VUS) present a challenge for cancer risk assessment and functional data will be essential to resolve many VUS. To address this, we developed a cloud-based environment to collate, curate, integrate and analyze all published functional data related to BRCA1 and BRCA2 missense VUS. Then, functional evidence criteria for pathogenicity were determined for each assay using the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) classification guidelines and ClinGen criteria. Our approach involved retrieving published articles reporting one or more functional assays of BRCA1/2 missense variants reporting variant impact on various biochemical and cell biological functions. Functional results were recorded using original authors' thresholds and categories, then converted to ordinal variables to harmonize: [0 = no functional impact], [1 = intermediate impact], and [2 = functional impact]. For BRCA1, we updated our previous published integration (Genet Med. 2021;23:306-315) with 14 additional publications, collating results from 53 instances of functional assays reporting functional data on 3,219 unique missense variants. For BRCA2, 28 publications were identified reporting data from 141 instances of functional assays on 4,759 unique missense variants. Utilizing a panel of 542 and 396 known pathogenic and benign reference variants for BRCA1 and BRCA2, respectively, we determined the sensitivity, specificity, and ACMG/AMP odds of pathogenicity for each instance of the assay. The remaining variants were assigned a relevant functional assay code weight for each assay instance. Our study successfully derived ACMG/AMP evidence strength from functional data for 3,040 BRCA1 (94% of 3,219) and 2,704 BRCA2 (57% of 4,759) missense variants. This comprehensive work underscores the utility of functional data in informing classification of BRCA1 and BRCA2 missense VUS. Citation Format: Paulo Lyra, Lucas Dalcolmo, Michael Parsons, Thales Nepomuceno, Samuel Brito, Nam Phuong N. Nguyen, Geise de Oliveira, Joao Paulo da Siva, Laura Caleca, Tanisha Taneja, Chunling Hu, Marcy Richardson, Maria Rossing, Aditi Hazra, Alexandra Martins, Sandrine Caputo, Gael A. Millot, Joanne NgeowYuen Yie, Marcelo A. Carvalho, Melissa Cline, Paolo Radice, Rachael Carlsen, Romy Mesman, Valentina Zampiga, Rehan Villani, Vijay Josef, Shyam Sharan, Kyriaki Michailidou, Amanda B. Spurdle, Fergus Couch, Maaike P.G. Vreeswijk, Alvaro N. Monteiro. Integration of functional data to classify BRCA1/2 missense variants: An ENIGMA project [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7325.

Abstract Many germline BRCA2 missense variants of uncertain significance (VUS) remain to be clinically classified as pathogenic or benign. Here we identify 70 missense VUS in the DNA binding domain (DBD) of BRCA2 that partially reduced homologous recombination DNA repair activity of the protein in a homology directed DNA repair cell-based assay. CRISPR/cas9-based knockin of these variants reduced cell survival of haploid cells and conferred increased sensitivity to the PARP inhibitor Olaparib. Sequence alignment analysis found that the variants were highly conserved across species from pufferfish to human. Structural analysis showed that these variants are located predominantly in unstructured regions of the DBD. Case-control association studies showed that the hypomorphic variants conferred moderate risks of breast (OR:2.85; 95%CI:1.43-5.88) and ovarian cancer (OR:3.37; 95%CI:1.30-8.54) that were significantly different from risks associated with known pathogenic and benign variants. Cumulative lifetime risks of breast and ovarian cancer among carriers were estimated at 25% and 4.7%, respectively. Age at diagnosis of breast cancer among hypomorphs carriers was 55 years of age as opposed to 48 years of age for carriers of pathogenic variants. In addition, the combination of functional and other genetic data in an ACMG/AMP-like variant classification model reclassified 39 variants as likely pathogenic. This novel group of low penetrance missense variants further calibrate BRCA2 variant classification methods and have significant implications for the management of variant carriers. Citation Format: Huaizhi (Gilbert) Huang, Chunling Hu, Jie Na, Mohamed Abozaid, Amik Munankarmy, Tara Rao, Carolyn A. Dunn Lumby, Paulo Cilas Morais Lyra, Ronan E. Couch, Benjamin R. Persons, Eric C. Polley, Rachid Karam, Tina Pesaran, Siddhartha Yadav, Alvaro N.A. Monteiro, Nicholas J. Boddicker, Susan M. Domchek, Marcy E. Richardson, Fergus J. Couch. Functional and clinical characterization of hypomorphic missense variants in the BRCA2 cancer predisposition gene [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr PR09.

Abstract Germline BRCA2 loss-of function (LOF) variants identified by clinical genetic testing predispose to breast, ovarian, prostate and pancreatic cancer. However, variants of uncertain significance (VUS) (n>4000) limit the clinical use of testing results. Thus, there is an urgent need for functional characterization and clinical classification of all BRCA2 variants. Here we report on comprehensive saturation genome editing-based functional characterization of 97% of all possible single nucleotide variants (SNVs) in the BRCA2 DNA Binding Domain hotspot for pathogenic missense variants that is encoded by exons 15 to 26. The assay was based on deep sequence analysis of surviving endogenously targeted haploid cells. A total of 7013 SNVs were characterized as functionally abnormal (n=955), intermediate/uncertain, or functionally normal (n=5224) based on 95% agreement with ClinVar known pathogenic and benign standards. Results were validated relative to batches of nonsense and synonymous variants and variants evaluated using a homology directed repair (HDR) functional assay. Breast cancer case-control association studies showed that pooled SNVs encoding functionally abnormal missense variants were associated with increased risks of breast and ovarian cancer (odds ratio (OR) 3.89, 95%CI: 2.77-5.51). In addition, 86% of tumors associated with abnormal missense SNVs displayed loss of heterozygosity (LOH), whereas 26% of tumors with normal variants had LOH. The functional data were added to other sources of information in a ClinGen/ACMG/AMP-like model and 700 functionally abnormal SNVs, including 220 missense SNVs, were classified as pathogenic or likely pathogenic, while 4862 functionally normal SNVs, including 3084 missense SNVs, were classified as benign or likely benign. These classified variants can now be used for risk assessment and clinical care of variant carriers and the remaining functional scores can be used directly for clinical classification and interpretation of many additional variants.

Abstract Purpose: Germline pathogenic variants in CHEK2 confer moderately elevated breast cancer risk (odds ratio, OR ∼ 2.5), qualifying carriers for enhanced breast cancer screening. Besides pathogenic variants, dozens of missense CHEK2 variants of uncertain significance (VUS) have been identified, hampering the clinical utility of germline genetic testing (GGT). Experimental Design: We collected 460 CHEK2 missense VUS identified by the ENIGMA consortium in 15 countries. Their functional characterization was performed using CHEK2-complementation assays quantifying KAP1 phosphorylation and CHK2 autophosphorylation in human RPE1–CHEK2-knockout cells. Concordant results in both functional assays were used to categorize CHEK2 VUS from 12 ENIGMA case–control datasets, including 73,048 female patients with breast cancer and 88,658 ethnicity-matched controls. Results: A total of 430/460 VUS were successfully analyzed, of which 340 (79.1%) were concordant in both functional assays and categorized as functionally impaired (N = 102), functionally intermediate (N = 12), or functionally wild-type (WT)–like (N = 226). We then examined their association with breast cancer risk in the case–control analysis. The OR and 95% CI (confidence intervals) for carriers of functionally impaired, intermediate, and WT-like variants were 2.83 (95% CI, 2.35–3.41), 1.57 (95% CI, 1.41–1.75), and 1.19 (95% CI, 1.08–1.31), respectively. The meta-analysis of population-specific datasets showed similar results. Conclusions: We determined the functional consequences for the majority of CHEK2 missense VUS found in patients with breast cancer (3,660/4,436; 82.5%). Carriers of functionally impaired missense variants accounted for 0.5% of patients with breast cancer and were associated with a moderate risk similar to that of truncating CHEK2 variants. In contrast, 2.2% of all patients with breast cancer carried functionally wild-type/intermediate missense variants with no clinically relevant breast cancer risk in heterozygous carriers.

10501 Background: Greater than 90% of missense variants in BRCA2 are classified as variants of uncertain significance (VUS). In addition, among the few known missense pathogenic variants (PVs) in BRCA2, breast cancer risk has been reported to be lower compared to pathogenic truncating variants (PTVs) (Li et al., 2022) . Herein, we aim to reclassify several missense variants in BRCA2 and investigate the associated breast cancer risk. Methods: A total of 450 BRCA2 missense variants in the C-terminal DNA binding domain (DBD) were evaluated for functional effect utilizing a previously validated homology-directed DNA double-strand repair (HDR) assay. The results of the functional evaluation along with clinical, structural, and in-silico data were applied to the rules-based ACMG/AMP criteria for variant classification to identify pathogenic/likely pathogenic (P/LP) variants and benign/likely benign (B/LB) variants. A pooled case-control analysis was performed comparing the frequency of reclassified P/LP missense variants among 82,372 women with breast cancer within the Ambry Genetics database as cases and 174,167 unaffected women within gnomAD, CARRIERS, and BRIDGES datasets as controls to evaluate associated breast cancer risk. Separate case-control analysis and comparisons with BRCA2 DBD PTVs, exon 11 PTVs, and known missense PV standards in ENIGMA were also performed. Results: From the 450 missense variants in the DBD, 137 (30.4%) were noted to be functionally deleterious and 313 (69.6%) were functionally neutral by the HDR assay. Incorporation of the functional and other data into an ACMG/AMP model led to the reclassification of 439 (97.6%) variants, with 131 as P/LP and 308 as B/LB variants. In a pooled case-control analysis, reclassified BRCA2 missense P/LP variants were associated with clinically significant increased risks of breast cancer (Odds Ratio (OR):5.6, 95%CI:3.9–8.0), whereas B/LB missense variants were not (OR:1.1, 95%CI:1.1–1.2). Similarly elevated risks of breast cancer were observed for BRCA2 PTVs in the DBD (OR:6.8, 95%CI:5.1–9.0) and missense PV standards in ENIGMA (OR:7.8, 95%CI:4.1–14.7). However, PTVs in exon 11 of BRCA2 were associated with a lower risk of breast cancer (OR:4.4, 95%CI:3.8–4.9) compared to PTVs in DBD, confirming the ovarian cancer cluster region effect in BRCA2. Conclusions: The study demonstrates that the HDR functional assay in conjunction with other clinical and genomic data can be a powerful tool that can aid in the reclassification of > 95% of missense variants in BRCA2. In addition, missense PVs in DBD were noted to have a similarly elevated risk of breast cancer as PTVs. The reclassification of the BRCA2 missense VUS and identification of associated breast cancer risk in this study will significantly influence breast cancer risk assessment and management strategies among carriers of these missense variants.