Villin is a tissue-specific actin-binding protein associated with the cytoskeleton of the brush border, which functions in the bundling, nucleation, capping and severing of actin filaments. In normal tissues, Villin is expressed in differentiated epithelial cells with a brush border such as intestinal villi, proximal renal tubules, oviducts, and seminiferous ducts. Due to the restricted distribution of this protein, the anti-Villin-1 antibody has been used to identify gastrointestinal adenocarcinomas. In combination with CK 7 and CK 20, Villin is helpful in differentiating metastatic colon adenocarcinoma from lung adenocarcinoma with rootlets. Additionally, Villin has been reported to be expressed in 85% of gastrointestinal carcinoid tumors and 40% of lung carcinoid tumors, suggesting that Villin maybe helpful in differentiating carcinoid tumors from other endocrine tumors.