CTNNA1 and CDH1-related diffuse gastric and lobular breast cancer syndrome: According to these 2020 IGCLC guidelines, HDGC is defined either by the presence of a CDH1 or CTNNA1 (catenin alpha 1) pathogenic variant in an isolated case of diffuse gastric cancer (DGC) or a family with two or more cases of DGC in first- or second-degree relatives [8].