Periostin is a matricellular protein encoded by the POSTN gene, that interacts with integrins and other extracellular matrix proteins such as collagens, fibronectin, tenascin C, and heparin, that are known to facilitate cancer development and progression through the promotion of cell proliferation, cell survival, angiogenesis, and the epithelial–mesenchymal transition (EMT). This evidence concerns the gene POSTN and cancer.