The CDH1, PTEN, STK11, and TP53 syndromic genes, which cause hereditary diffuse gastric cancer (HDGC) [17], Cowden disease/PTEN hamartoma tumor syndrome (PHTS) [18], Peutz–Jeghers syndrome (PJS) [19], and Li–Fraumeni syndrome (LFS) [20], respectively, and which are also BC-associated CPGs, were excluded from this review. The gene discussed is CDH1; the disease is PTEN hamartoma tumor syndrome.