Panel testing reveals nonsense and missense CDH1 mutations in families without hereditary diffuse gastric cancer

BACKGROUND: The reported penetrance of germline CDH1 mutations is high in families with hereditary diffuse gastric cancer (HDGC). Men and women have a 70% and 56%, respectively, cumulative risk of developing diffuse gastric cancer by age 80. Women additionally have a 42% cumulative risk of developing breast cancer. Due to the high penetrance of these mutations, prophylactic total gastrectomy is currently recommended for CDH1 mutation carriers. However, whether everyone with a CDH1 gene mutation is at risk for HDGC is not clear. METHODS: Mutation identification was performed by next‐generation sequencing. Mutations and variant status was confirmed by Sanger sequencing in 11 family members. RESULTS: We present two families with pathogenic CDH1 mutations. The first family carries a novel truncating, nonsense CDH1 mutation that we were able to trace for three generations, but reports no family history of diffuse gastric cancer. The occurrence of cancer in this family deviates significantly from the expectation for HDGC. The proband from the second family presents with breast cancer and carries a previously reported pathogenic CDH1 mutation, but also reports no family history of diffuse gastric cancer. CONCLUSIONS: Our study demonstrates the need for further analysis of CDH1 mutation penetrance in order to better counsel asymptomatic CDH1 mutation carriers on preventative measures and general care.