Claudin-1 (CLDN1) is a transmembrane protein and a critical component of tight junctions, which regulate paracellular permeability and maintain cell polarity in epithelial and endothelial sheets. Beyond its structural role, CLDN1 is involved in cell signaling, proliferation, and survival pathways. It is frequently overexpressed in various cancers, including hepatocellular carcinoma (HCC), colorectal, breast, and lung cancers.