Although the monoclonal antibody D2-40 has often been used as a marker of lymphatic endothelium to identify tumor emboli in lymph vessels, it was recently found that D2-40 immunoreactivity was also detected in the basal cell layer of the squamous epithelium, stromal myofibroblasts, mesothelial cells, and lung cancer cells [74], [75]. This evidence concerns the gene PDPN and lung cancer.