The estimated lifetime risk (70 years) for (1) the development of breast cancer is 85.2% (71.4%–99.1%) in individuals with Cowden syndrome and 45% (27%–68%) in individuals with Peutz-Jeghers syndrome; (2) the development of colorectal cancer is 48% (30%–77%) in individuals with mutations in hMSH2, one of the genes involved in Lynch syndrome, and 9% (3.8%–14.1%) in individuals with Cowden syndrome. This evidence concerns the gene MSH2 and Peutz-Jeghers syndrome.