Podoplanin, also known as D2-40 or M2A, is a 38 kDa type I transmembrane mucin with multiple O-glycosylation sites. It is highly expressed in lymphatic endothelial cells, but not in blood vessels. In addition, it is also expressed in a variety of cells, such as mesothelial cells and type I alveolar epithelial cells, follicular dendritic cells, reticular cells, ovarian and testicular germ cells. Podoplanin is a very useful marker to distinguish malignant mesothelioma and adenocarcinoma, seminoma and follicular dendritic cell sarcoma. It is also the main choice to show and quantify lymphatic and intravascular tumor infiltration.