PDPN and malignant mesothelioma: PDPN is highly expressed in various intractable tumors, such as lung cancer, malignant mesothelioma, malignant brain tumors, and esophageal cancer; however, it is also known to be expressed in normal cells, including lymphatic endothelial cells, alveolar epithelial cells, skin basal cells, and renal epithelial cells.