Keratins are a large family of proteins that form the intermediate filament cytoskeleton of epithelial cells, which are classified into two major sequence types. Type I keratins are a group of acidic intermediate filament proteins, including K9–K23, and the hair keratins Ha1–Ha8. Type II keratins are the basic or neutral courterparts to the acidic type I keratins, including K1–K8, and the hair keratins, Hb1–Hb6. KRT18, also named as CYK18, PIG46 and K18, is the most commonly found members of the intermediate filament gene family. KRT18 is a type I keratin which is found primarily in non squamous epithelia and is present in a majority of adenocarcinomas and ductal carcinomas but not in squamous cell carcinomas.