CDH1 and CDH1-related diffuse gastric and lobular breast cancer syndrome: The main gene involved in hereditary GC is CDH1, encoding the E-cadherin protein [7], whose germline mutations are responsible for Hereditary Diffuse Gastric Cancer (HDGC) [8], a genetic syndrome linked to a lifetime GC risk of 42–70% in male carriers and 33–56% in female carriers, who also have a 39–55% risk of lobular breast cancer (LBC) [9,10].