Until recently, CDH1 was the only known susceptibility gene associated with HDGC, but, in 2020, the IGCLC recognized CTNNA1 as an HDGC predisposition gene and recommended CTNNA1 testing when no CDH1 pathogenic variant has been identified [2]. Here, CTNNA1 is linked to CDH1-related diffuse gastric and lobular breast cancer syndrome.