CDH1 (cadherin 1) type 1, encodes E-Cadherin and is involved in epithelial cell-cell adhesion, cell signaling, differentiation, and polarity. CDH1 germline mutations are associated with hereditary diffuse gastric cancer and somatic mutations are found in gastric, breast, colon, and non-small cell lung cancers. Simple mutations in CDH1 are seen in about 2% of all tumors, but are common in breast and stomach cancer (11% each), where they define a specific type of breast and stomach cancer (lobular and diffuse-type, respectively). Pathogenic CDH1 mutations are used in the diagnosis of diffuse gastric cancer, in additional to lobular cancer of the breast.