Cytokeratin 7 (CK7) is a protein that in humans is encoded by the KRT7 gene. CK7 is a member of the keratin family and it is specifically expressed in the simple epithelia lining the cavities of the internal organs and in the gland ducts. The type II cytokeratins consist of basic or neutral proteins which are arranged in pairs of heterotypic keratin chains co-expressed during differentiation of simple and stratified epithelial tissues. IHC staining of cytokeratin 7 is useful for carcinoma diagnostic especially for differential diagnosis of urothelial, lung, breast carcinomas to colorectal or prostate carcinomas. CK7 is especially marker of lung adenocarcinoma. Pancreas is the good tissue control for CK7.