According to the new guidelines, defined in 2015, CDH1 testing should be considered in patients who meet one of the following criteria (including first and second degree relatives): (1) 2 GC cases regardless of age, at least one confirmed diffuse gastric cancer (DGC); (2) one case of DGC before 40 years old or (3) personal or family history of DGC and LBC, one diagnosed before 50 years old. The gene discussed is CDH1; the disease is gastric cancer.