Abstract 1282: Genetic basis of hereditary gastric cancer: Beyond the CDH1 locus

Abstract Importance. Hereditary gastric cancer (HGC) is a rare, autosomal dominant susceptibility syndrome characterized either by early onset diffuse gastric cancer and lobular breast cancer or aggregates of intestinal gastric cancer. The genetic etiology of <50% of families classified as hereditary diffuse gastric cancer (HDGC) can be attributed to pathogenic germline mutations in the gene CDH1 (which encodes a crucial cellular adhesion molecule, E-cadherin). Unfortunately, the genetic basis of CDH1-negative HDGC families and all familial intestinal gastric cancers is unknown. Objectives. 1) Determine whether pathogenic germline mutations in genes related to upper gastrointestinal disorders (UGI) are causative in HGC and 2) show that a targeted multiplexed next generation sequencing approach is effective and efficient for detecting such mutations. Methods & Participants. 115 probands from families who met clinical criteria for HDGC (n=108) or FIGC (n=7) were included. HDGC participants have all previously tested negative for CDH1 variants. A custom panel of 55 genes previously associated with heritable UGI disorders was designed through literature research and collaborative efforts. The germline DNA of probands from each family was sequenced for all targeted regions using the MiSeq platform. Candidate variants were selected based on likelihood of pathogenicity (protein truncating, rare/novel pathogenic missense variants) then validated via Sanger sequencing. Tumour materials from mutation-carriers were analyzed for loss of heterozygosity via immunohistochemistry and/or second hit analysis. When available, germline DNA of additional family members was collected for segregation analysis. Results. We have identified clearly pathogenic mutations in unrelated HGC families, including two protein truncating mutations each in CTNNA1 and BRCA2 genes and two rare, pathogenic missense mutations each in SDHB and STK11 genes. Additional protein truncating mutations were identified in moderately penetrant genes ATM (4 families), MSR1 (2 families), and PALB2 (1 family). Overall, 13% of families included in this study were found to have pathogenic (8) or likely pathogenic (7) mutations in genes included on our custom panel. Tumour material was available from probands with truncating CTNNA1 variants, revealing distinct loss of protein expression using immunohistochmistry. This further supports the likelihood of pathogenicity. Conclusion & Relevance. Using a targeted next generation sequencing approach that significantly reduced sequencing cost while simultaneously improving turn-around time, we show that HGC families can carry pathogenic mutations outside the CDH1-locus, including genes commonly associated with other UGI syndromes. The genetic basis of the remaining families likely lies in yet to be discovered susceptibility genes or, in the case of HDGC, additional abnormalities at the CDH1-locus. Citation Format: Samantha Hansford, Hector LiChang, Pardeep Kaurah, Michelle Woo, Karey Shumansky, David F. Schaeffer, Giovanni Corso, George Zogopoulos, Steven Gallinger, Hugo Pinheiro, Franco Roviello, Carla Oliveira, David Huntsman. Genetic basis of hereditary gastric cancer: Beyond the CDH1 locus. [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 1282. doi:10.1158/1538-7445.AM2014-1282

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