Claudin-5 is a member of the claudin family. Claudins are integral membrane proteins and components of tight junction strands. Tight junction (TJ) strands serve as a physical barrier to prevent solutes and water from passing freely through the paracellular space between epithelial or endothelial cell sheets. Claudin-5 is an endothelial cell-specific component of TJ strands. It has been used as a marker for endothelial lesions. Claudin-5 is also found in bronchial and lung epithelial cells. In tumors, Claudn-5 expression has been found in lung adenocarcinoma and squamous carcinoma. Strong membranous expression of claudin5 and claudin7 differentiates pancreatic solid papillary neoplasm from pancreatoblastoma, acinar cell and endocrine tumors.